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I ·-~~) LAVA-DOME GROWTH ANb-"EXPLOSIVE VOLCANISM IN THE JEM~Z.N'JOUNTAINS, NEW MEXICO: EVIDENCE·FROM·THE PLIO-PLEISTOCENE PUYE ALLUVIAL FAN

H.l'\. TLHHEVILLE·. DA!v10\! H. \\'AHE~BA<'K anci STEPHEN ~EI Y

Abstract

'Llrtwvillr. HS .. \\',m·~back. D.B. and ~it.:-)., 1\11\!1. l.;t\·;, Jumt· ~row1 h antlt>xplosi\'1' '"t..Hni>m in the .JrroW7. Moun· 1aon<. New :-.t,•x i< •.: E\' idr·nr·t• frorfl1 ht• l'liu l'l•·r•l• •n'll<' l'u,·t· :.llol\·ial tan .! \ 'u/nrnu/ I ;,·nthi'T'II /{, s . ;U): ~~;-; :!!1 I Th.., l'lio·I'It•r,tok'f'llt' l'uyl' Formati<•ll. north·fi'IIIT:II ~ ...... :\lnlt'•l, i> a :!00 km1 \'ol,·an•lJ,:I'nk nliu\'illl fan !>hl'rl t•astward from 1ht' T~t·hin>ma vnlcanir t·rntH. part ul tlw .lt•rnt•z Mountain> \'nkanif: fidtl. Tht• fun cunt.ain~ > lf1 krn · •>f v,Jcanicla~t ic ma1rri11l dNived from rln~t'l~· span·d l;ovil rlnmt'~ in t lw nor1lwa~t••rn Jl(lrtion of thr- T~t·hinmla n•nlA'r. lnt!'rh .. dd<·d in thP fan Sl'dirnents arP at l~a~t \!~• prirnar:v p~·rt•dastic unit~ from t·xplosiw Pntption~ of dadtk and rhyoliti<' la\'11 dnmt•>. Tt:phra •wcur mainly lb pumit'l' litlls hut in .. l;sdr,. >t•\'t•ralpumict•nu~ i~tnirnbrite~ and twu thit'k proximal bl•X'k·and·a~h p~·roclastrc flnws. Th«> uppt>r pi!rt of t.ht· fan al~n rontllins rhyolitic plinian drposits enrpiE'tl frum suurct's in tht> t'fntral portion of tht' .J .. nwz firld and hasah rc ash dNin•d fmm thr n•ntral Hio <:randt> rift. Fanj!ltlmt-ratic !pyroclastic and epidaMic J faries t>Xhibit t·onsidNahh·lllteral variatiun. I' rima!')' lt'phra depo!liL~. huwenr. pro"idt' a stratigraphic· framt·work f,,r rl'nlJI>trurtion nfthl' ,;rnwth of indivirluallava dome~. While nnl\ \'olcanic domt•;. and Ja,·a flow~. are t'XJlllst·d in thl' Tsdncomrt <:•·ntN. l'uyr tt·phra layers shuw that vukanian, subpli· nian and plinian a<:ti\'lty. an<l bltx·k-and-ash pyrnt'las1 it· fl,,w~ acrumpanit'd manydomt>-fnrming evt•nts.lll'jV'aclatinn of thl'l>P. iava rJ,,m~s product-d cnarse-graim-d dl'hris flow~ dominatt•d hy l.t\'il und dome c&rapace da~lS. From th«>~ epidasl~ i1 i~ fhls~ibll' to idront ify lithnlngrr~>ofla\'11> that arr t•ither currrntl~· buri«>d or ha\'P bt>en ohlit~ratffi by ernsrnn •lr hy cnllapst• nf the \'allt-> calderas.

ThE' pr~rvali<>ll of Puye deposits n•ll('cts '"flo' high rate~ of aggradation and l(radual down -faulting iu th~ F.spari•>la hMin of tht- Cl'n1ral Hio r:rande rift. Thi> rt't'ord ,,f 1'.\'fllt'i<l>l it' illlO (·pidastk dt•Jlu~i1 inn ullc·W~ dt•lailt'd llll!•l"jlrl'lat ion ••f t h" e\'ohrtinnnf 11 \'olnmic rt>nlo•r from its p_rrod .. st ic and cru~iun prt;ducls. and is tht• first Pxampl•· of n \ nlcanol(t>ni•· alluvial fan in an mtracon1 mt-nr.al rift St'll in!! 1o bt< rlt•st·nb.,rJ in do·lail. This ~tudy t·mpha~izes that mtl'rpr«>tation of any ancirnt vukanit' t('rrain hai\E'rl snlt>ly upon data dt·m·1·d from mappin~t. rarlinmPtric datin~:. and ch«>mit·al analysi~ of la\'a" or Histin!) denudE'<! edifice~ is likely It• grl'atly undNN.timatt' hot h tilt' roh• oft•xplosi\·e mlranisrn rnth!' build· up nf ,· .. Jcani,. C!'lllt•rs and ~ub:;t>qut•nt ~tirua1rs "( tht· vohurrt•S ,,f matNial product-<!

Introduction

Explosi\'~ volnmism Ot'l'urn·d throughout the J:L)-million yt•ar dt>\·elopment of the .Jemez

•Currl'nt ;1drlrt'~': IJepttrtnwnt ofC;t't.olo~:ical:o; ·i~·nt·t·~.l'ni \N,ity ni Tt'Xd' a1 A•r•llll. :\u~r in. TX ';I";):; ';!111!1. t ·.~ ,, .

Moun tHins volcanic field ( .JMVF; Fig. 1 I of nort h·n·nt r&l t-;ew Mexico. Mo~t work in this art> a bas coneent r<lied primnrily on either tiH· voluminous Quaternary rhyolitic ignimbrit('s !Smith and Hailey,l966; lzettet ai..I981 J and relatf.'d cahiPra!; C Smith anrl Haile~·. 196R ). or on t lw pet rolo:.,~· and lii.!P r<•lationships of long·

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livt>d l'pisode:- of lav;1 t•ffusionand donw growl h ((;ardrwr et al., 19Hti; Singer and Kudo. J!llili: Loeffler ~t al., 1988), particularly in the l'ali1 .. a Canyon and Tschicoma Formation sequences t Fig.:! 1. A nPglect('(l nr<>a has hE'Pn ~tt.dy oft he t•xt t·•)si\'l• vn!nmida!'t ic !'(•quenrP!' that r('lat P

(•rupt i\'1! activity and Nosion of individual .Je­nwz volcanic cl'ntt>rs to Hio (irandl' rift-con­tn,\lf·d st·ciinwntation.l ktaill'rl rincunwntation oft hese >'i"!Jilt>nces is crucinl to undPrstand:ng t h<• ,·okanolul-' i<·al t>Vt ,Jut ion oft hilS liPid, as t lll'y contain abundant pyroclastic depo~it~ int!·r­st rat ili\•d with epidas\ ic debris. Tht>s<• n•lat ion· ship:- are ran·ly p\·idt•nt in the Ct'ntral .Jt>nwz tield hut lH<' particularly well display('d in t h<• l'uye Format ion, a h1rge vokanidastic fan sht>d irom the Tsrhicoma volcanic cent-er in the nort h<·astt:>rn part oft he field (Fig. 1 ). The Puye Formation is ideal for study because of its ex­n.•llent exposure and dose spatial, temporal, and lithoiogic assvciation with the Tschicomn cen· ter. Pyroclal'tic and epidastic depol'its in till' Puye fan, t hNefore, provide valuahh.> insiAht into the history of Plio-Pleistocene Pxplosive t>ruptions and lava dome development in the northeastern .J MVF.

Tschicoma volcanic center

The .Jemez Mountains are situated on the western margin oft he Hio <~randt· rift at it!' in­tersection with the .Jt:>mez Lim!ament (Fig. I).

r:rupted products have been divided into three stratigraphic groups representing three succt:>s­l'in> periods of magmatic evolution and erup­tion (Bailey et al., IB69: Smith et al., 19i0 ). The proposed divisions MP the Keres (including t h<· Paliza Canyon Format ion), Polvadera ( inrlud· ing the T!<.chkoma Formation), and Tewa (pri­marily HandeliPT Tuff and post-caldera lava domes) Groups, in agl' sequence (Fig. 2 l. These volcanic and volcaniclastic deposits span the period 1 :u1 to 0.1 Ma I Gardner et al., 19RIJ).

The Tschicoma vole a nit· center ( i.40-:l.9 Ma; (;:udner t•t al.. I:IRfi; SingE>r and Kudo, HlHii; Balclridgt• Pt al., 1!-1~7) contains > i)OO km' of

dariti!' lm·a l1ows and donws in th(• n<JrthPrn and ea:-tt•rn ,J<•nwz Mountains with suhordi­natl' amounts of 2-pyroxene andesite, rhyoda­cit<'. and low-silica rhyolite (Baldridge and \'ani man, I!IX!i; IJavid Broxton, unpubl. data). And<•sit it· la\'as gt•nl'Tillly undl~rlit• t lw dncitk and rhyoda,·it ir hl\"as and doml's 1\~uc:h oft h(• :-nut hwo·:-1 <·I'll pari nf t h<• Ts< hirornll <'en! er has IJI·('I} nhlifl•:·;tft•(l. initially by formation (If the

T.,Jt>dc: Em;Jaynwnt (fi,.;. I), .nnd lat<'T by col­lapse of I hl \'all(·s I I or Toledo; Smith, 1979) and II calclo•ra:-o at 1.4 and 1.1 Ma, rt•spectively 1 BaJJridgt• and Vaniman, l HHfi; S<·lf ct al., I !lAo l. Sun·i\'ing volcanic fi.•atures oft his cen­tl·r s\ll!!!l'St a st ron!! tectonic control on mag­matism with tlw early development nfhasaltic :mel andt>sitic strat<lVokanoes in tht:> north· wel'tern .JMVF and l1lter growth of dacitic and rhyoclacit ir dome complexes farther eastward tSingerand Kudo, 1986: Baldridgeetal.,l987). Ma~matir activity in the northeastern .JMVF

ht'gan to wane het ween 4 and 2 Ma as several small. isolated lava domes (i.e. pumiceous flank domes 1 were emplaced onto Tschkoma For­mat ion deposits (Fig. 1 ) . These domec; form the El Rechuelos Hhyolite and Cerro Ruhio Quartz Latite 1 Fig. 2; Bailey et al., 1969), the latter se­qut:>n<'e more recently recognized as part of the Tsehicoma Formation (Gardner et al., 1986). The youngest El Rechuelol' Rhyolite lavas are di1<tinguished mineralogically and chemically from tht• "oldtor (Tschicoma I rhyolites" of Loeffler et al. ( 19AA), but are mineralogically similar to several tephra deposits in the upper Puye Formation. F.pklnstic material from this t'l'l\tt'f. hnWl'\"£•r. is poorly represented in Puye dPposit:- rlue t u topographic harriers existing at t h(' timl' of <•rupt ion of these domes.

Tlw Y•'ung<•st euptives hitherto reported from thl• T,;rhicoma ,·olc.anic c<'nter are 2.9 Ma I Baldridge <·t al., 191fi' ), although this study emphasizes that portions of th(' center re· maim·d act iw up to :l Ma (or lt:'~l'; Turbeville. Jl}~6), and that t:>vid<•ncf:' for younger dadt~ and rhyodarit t' lava domes ( i<i JH'(' deHtroyl'd by eru-

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,;ion and caldera collap,;(•l ,.ourvin·~ ~->xclu~iq•ly in the Pu~·e Formation.

Thl• Puye Formation

The Puye Formation iGrigJ!s. 19fl4; Manley. 19i'H. 19i'H: Wareshack and Turhevil:.:.•. in pn·,;~ 1 i~ the exposed upper part nf at hick volcanidnl'· tic ~NJUI'nce emplacE'd <'OiltE'mporam•oul'l~· with 1 ht· Pliocerw df'\'E'l<)pment of the 1\l'hil'l)ma volcani.: center. The Puye Formation contain:< > l.'i km' of Plio· Pl{'i,;to<·<.>ne allu\·ial,;t•dinwnt ~ <i<·ri\'l:d rmtinlv frnrn (;w;t rl<,nw~ in tlw north·

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1'1!! 4. A :\ppro~ irnah• ,·ulurn•· Jlf'H'CIIhll!t'~ nf ro• k 1\'1"'~ ''"""! a• ,·p;l'l:t-1~ IM·t· Tahh· :! 1 in l'uyt• lund .. mt·rall·~ I' alut·~ dt•nvt'tl frum r<·)'rt'>'t•nl uti VI· t·uunt" ol c·l'"' s ·• I If 111111: If== ;!110 pN dt•po~il. B. \'ari:~t io>ll~ mtlw pc·rt·o•llta)!t' ,,f I ht·,.•· da,.ll\'l"'•lll•lw<•<•ll t ht•l<>w<·r and UJ>Ili'T purl ion• .. r tlw nwdiallar; f•ll'i•·~ uf 1 "" l'uyt· F••rnutt ;.,n t:-.-.~· F1gs. !,. fl 1.

<~astern part oft he Tschicoma center I Fig!'. I. ;{). Thi!< alluvial fan records a hi!'tor•· of <>xplo· st\'t' art ivity that produced <thundant dacit i<· to rhyodaritir tt•phra (TalJI<. 1) during the later dt'velopment of the Tschicoma center j :!.5-1.9 \1a: (;ardn<>r et al., 19R6: Turl:~e,·ille, I 9M .1. The wt•ll-exposPrl parts oft lw fan show nwdial to dist a! ,·nlt·:mo!-(('tlie fanglomNat ic faci<>s with abundant epiclast ic mat<>rial emplaced a;; !'uh­aerial mas,; flow,; and hyperroncent rated flood flows tt·.f .. Smith. lBHf)). ,;tream channel de­pn~.ih·. and sh(•et llond nml!lonwrntel'. Thf:'st• ,.;l'dimt•nts an• intl'rbedd<>d with primary and rt'· dPpm.itt>cl pyroclastic depositfi and. to a lesser 1·xt ent. a really ext<'nsive mafi1· )u\'11 flow!' und associatt·d hn·ccia~. In addition. lat·ust. rine dt•· pu:-:it,; 1 including abundant wat(•r-lain l~·lsic nnd basaltic l!~phra) art• \'Oiunwtrirall~· significant 111 dil'tal part,; oftlw fan.

Explo>si\'t• {'TIJpt ions that Hl'l'fllltpa nit'cl t lw

i'

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II

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l't~r;, 1 • ~r .• ~ d~nlt•

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l' .. r,•il '•..:ht ~r,·~\ d." irt·

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l.ar~· Pin~. l!l"nH·w,·ry>l> nlld •Jll "'11 h I,I,.J,,.,.," upx 111 an llllf'r>lll•almatnx .,f ~uhp<~raiJpf pia~. mirrulit('~ in cl;u k I!Ti!." 1!111~.-

!'un:!:or !11 l\'po•l t•x,·t·pr I:Hil I; l.tr ;o·r ;•hon-,..,_,·1·· .1no! .t.,rnwrh lllll'ah·d 1.1hrr ... •tl.· r.,,.., hill r.·r·l.on·d J,, F, ... xuJ,.,

Eql~t,:r.uullar pJ qt.t t'f'X •PX hh !Ji Jd,, 11 111" ~: •. 1lt1~ ~~t -! .. f,h,. ra: . .f"r~tl\ ••ru rt!•·d '''••· hrh ... ', ·r! l11•ph~·r u· •. ;!I• •llit·r••,·r\ -.r .. ~.trt

:\hr·ru.•:.rt~ b.twi:-of J.,:.J.c .. -.\'. lltlt r•:llf~- l'·•••r ard ·kll"' h 1111• rtlh~w :--•·n Jlt·l.n.t.l•l.·u- . .r,•f Ft• "';,ft. .. 11~ Jha:-.dlt·i t.thri,. ;·•fH;IHf ''I'' \\HluH, I'' pr: .. r:l:-

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l'i.•.: ll'•·l!•ton·•l> '"I': .. I I nan• "11 :, •··J•:.tlll 'I'' .. ;,.,ltl•· 11111 rupho·n 111 llo.ol r.>. .. r >! .1lolo\ pi q>x HI IX 1111 llli•Tnhlt·~ Ill~ •• ,~ .. : ol pia.;. I!ITt·T~TII\\ r j, .... I 'lli:J&•IIl

Fdtruu ... ·lltt·.\ hll!ldt•d t f'' r. ,, f:t,l u· lrkt· i lt·:\1\lrt•. ~ph• rulill• ;•II.\ dt·\·rt rrfll·ti gru:uuhna ..... Jad\:oo. pLu;: .thund "onttlt'!-<!ft.' hrhi,·~ aud iolrt.:P f ··~:: :ntn) J: .. ulartod Ft~ uxhf,. pht•nn• r.\'!-<t .. .

l'n;:,tnl .. nh .. phw~o· lt·xrnro·" 11 h >lump~ pia::. Ia fir, and h.l"·hi hhl iu •pho·rt•lin. ;olh Ill·\ 11 rif!f•d i :tih r••hrt·n·idft•d J ,.;rol:Jldlti:t~·< 1.tr:1t' io!rt'l•ll htnt itt: ,·r\':o-I.J)~ otft' I tllhJlH':IU\1..,

.:""HJ!:tu Til t~-pt· ... I ,:nd I J t•\•'t'JI! ~~., d, .. , ;u. :iv •. ~ .• r •• r t..Hhfll~t.: and IJI'('IIfff'lh·f·ol r~lf).!f• hu,l Jll' t·rv:-.t,a)~ 1n clctrk r•·d f•rp\\ n ~rn,lndnl.·t!'oo ...

I'\ n cltt~t i, likt· crutJndrna ...... ''a'\ !'ooh.url 1tkt· h atur, ... ••utlnlt' a \\c·.tk !ln\\ Jmnduu:; LUI hrnwu <J, 'irrif.,.clrnarrix o·xhihrl> "~lro•t.-/;o·d •kin' .tppo·;~r:tltn·:

I mil\ i<hal ba,alr ,.. < la·l~ ( · :;il,·m rli.otll I 111 hnir,,l ho·nn,tlh· alt.·ro·d at HI h:lildo•rl. ~-:r.:~· lor .. wn l!ruundrna~ ... : \HltJ""IIill ~~.t·!t·t;tl a,.:;.:rt·c•,h·!'oo uf hl.;uit·d au~;fc.•

I lb: '"ell\ I' rl .. \\ It· X IIIII' lll'flilrlt·d h·· pl.t~ 111kr. oLio''· pl .• ;: )'ht·lliii'T.\''!' ,, r• •II;: I\" •·llll· 1\ ··d."' JIX. n.: JJ)h:rohtf'~ in hrn\\11, J,!lfl!'oo:'Y ..:r.at:ru.htl.l~~; hi,..:h ('r\~fal J.!f;t~!'- raflt•.

L;r,.:o· pl,tg.l!i.,mt-rut·n·,r~ a11d >Uh.,phllw :ur,:ih· in ~!ray lorowo; ~:la~,,.l!r"'""'""'" \\'t!h I••\\ pial(. mi,·rulitt4~.

l.ar~t- p!..tJ!. J!l••nlt•rot·!'"."~ts in dc:n~t·.nru·nt••rl·illlt·r ... tlfJal Jlllt r~~lii«•J.!r,,undma~~. L•TJ.:t· fil J1hl cry~t.JI:o. and qtz nucrnph,·no,·ry~oo.t:-o

I~IT,.!t' pial!. plll'lloi('T\'Sl> with hy-hi- hlol 111 ranclomly <•Tit'lltt•clmh·rulitu rn:ll nx. nil I'' ·qf mu·r .. ph••n. in radiating ur d<>mlrili( ··h:•l!'r;.

l.at !t!'·rh,·u<:illt'ilt' with pial( ph~n. rtmnH·d ll\' rwrl hir h or CT:tii••Ph.Hio· m ,.rgno\\ I h, iJ: \H·akl~ rlow-bando~d. clark gra~· .:r"undmtts": K·r.•lcl•p.lr all••tnaluu,ly ahundartl a~ larp· t.,hulilr ,·rysLul~.

Fl••\\ han:!t•d la•·;t rl.~>l" 111 dl"lillt'll.• I"'"'" •••u~. ltllfrohn·n·ialt·tl rnatn~. H\"•l;d and 'Hill• rra!!nh·rtt" t.'•lll:rn••u. ·-·----*--·- .. -~-·-· --··--. -~···~--··-· ----··--·---·"--- ---···-·-

gro\\'t h of Tsc h il'IIIJlH la\'a do •n•t·:< \Wrt• pro •hahly in:<trurnental in remobilizing largt· portions or talu:H'O\'t·rE:"d 01•11w ,;urliH't•:< !c.f .. Ho:-(.'. 1!1.~7: :-irutt. Hh7 I. Stt:t'Jl topography and sporadit· 1 possibly rpi!'-odic) llood lrt•qu£·nc~· and runotl in this H•r·Ji-nrid region ( ht'llt·y. H17!l: Dt•thit·r and Dt'm:'ey. Hl.~·ll contrihutt•d lo tlw llppar. <·nt 1.\· high ('f\•~i••ll ratt':o a:;,;.oriatE<d with tlw denudat inn of t !w:-;t• donws. pr.,viding a bun. dant t•pirla:;tic matt>rinl to tla· ~::r .. win).! f;ln. For

thi~ rt·a!'-r•:J. \\'(· ht•lit•\'f' tlwt tlu· l'u~·e allu\'ial far. ndt'<JIJ:ttt·l~ n·prl':o:t:nt,.: an inn•rtt•d ,.:Irati· graphic :<ll<'t't•:;:-; j, >II n f PI in ·I' lt•i:;t o<'t'llt' la\'a dt!lllf· dl•\ t•lnpr:ll'nt iilld f'fo:;iPn in 1 h<· north· (·il,.lt·rn part oftlw '1\('hicollw n·ntt•r.

l'u~·t- Formationl•pida:;tic dl.'po.;if!i('<'lltain a hi:.: hi~· \'aria hit· :-uitt· of Ia\';, litholngit·,.; 1 Table• ::: Fig.~ 1: thi:< 1:0 in ;;harp ,·ontra;.;t to tht• t•X·

pu,..f•d rork t_\'Jlt<:; of t lw T:;rhil'orna l'rllfll i\'t'" 1 Hii!driclg!· and \'animan. I~'-"'' 1. l'lll,.rtll·

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lluvial .;trati·

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Table he ex· lpti\"£·" tfortt~·

i I I I i I ' I I I 11

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natt·l~·. dJrt•t; , nrrt L:; ;.,:; • •! tan dt·P""":r :-- ''· ~~ h t lw rurr~nt 1\· d,·nlldt·d '- "'' <IIlli.' \'t·n tt-r 1~ ~ rt·;ll h· 1nhiL;~ed h\ bnHlt·d 1 :-p .. ,..ilrt·Jilth•· an·.i ''h·n.· lan1 lltJ\.,.!' and fan ~edinwntli i;1tc·rfinp·r. :-;1m· ilarity lwt Wt•ffi ;1\ ai!ah:t· lllirwr;lln!-!i•·al :u:d p•odwm ic a J,· h.lr:t< • • n-t '' - nf l'u.' t· r.-p h ra and T,.;··h inm;a l;.\".1,.., !.· .·w<·\ I"L :-t r• •~>::I~· "''PI'• •rt' t ht· t'lllll t•mpnr;i!Jt·ll .\" • •! t ht·.~t· rnck.' I,.,.,. l,,.j, ''' :.

Tlw l'l'~l· fa:i :1~,, .• ••Lt.1in:- h:t,..:dtic a:-h de· rl\ ... d from phn·<il• ll!l<l!!l:l;ct lt" l"fllplton:- 111 t Itt· (\·rrtl::- dt·l Hiu \"okani• fit·!d 11f tlw n·ntral H1•• <;randt· rill 1 F1~"· l. ·~: Alli>t·lt·. 1~t7~t: Fi,.;lwr t·l al.. 19.'i-t 1. Tlw t"tJ!llbirlt·d intlll•.•nn•:-nlcnnll•Jn P• raneou,.; ,.,)kani-m tr .. :n 1 hl''-l' t wn adjan·nt ,·olcanir n•ntpr,: an.· rl'tlt•rtt·d in tlw f;lll b~·tiH· dt'\·E'Iopmrnt of di!"t ill\1 in• cyclical depn"i 1 ion a! !'Pyut>nn•:o:. In ~'"''t'lll't-. tlw T.;chirnma n•nt<'T ~teadil~· >-uppli•.•d lar~t· quantiiil·~ <>f l·ol­canic!astic m<IIE'ri<~l 111 tla· pn1grading fan. wh£>rt'a" \'olcani~m in till· <"t·rro,: tidd :;t ronl-!l.v intlue.nct-d :<(•dinu•nta!ion fwm th<' l'a!'tl'fll ba,:in margin. 1>;.· lakt• d,.,d.,pnwnt mHI , ..• ria­lion,; in lt~cal tlu1·ial h,l,.t·IPH·k

Pyroclasti<' ~~rat i~raphy

Analysi!' and l:orrt-lat i•.tn of primary pyro­dastic deposit~ in the Pu~·p Formation lsi.'P /)('-

: .. ·.\ 1 - '"·.~,:c·-t til;ot ,.:t•\"t·ral t•xp!.,,.,,,. •·r:lptioll,. ! r"m 1 h·· 'J" ... .-turonu n•nrl'r prndn.-t·d v.·id•• -l•rt,a.i t:tll bl:inkt•t:< ano:-,. tht· !!ro:wing I•uyl• fw1. Ln,·a lm·d prt·!'E'r\'at ion of thE'!<{' de;>osits tkpl'ndt·d ~>:: 1 !J,. rapid ;w,·umll!.!ll• •L nl a pr.•· ; I'll j\ I" '01\ t·f nf •·pida:-111" dt•hri:" f H ;H)d I~ ion; I! p1ro..-l:t·-lll" •H.;t,·ri;tl Till' <•h"t'lh't· ol <'t•t'\;ll I•\ 1"\Jt",;o.,! it' d·.·po:-it~ IJt'\·orult ht· !inl!!' 1111 iJj,- ;ll· i '' ial '' '!t"11: '"~u·:-t,.; 1 hat 1 ht· ''ITrto· mdin;: t·ll ,·ironn.t·nt:- \\t·rc• th~·n•lon• not :.uit;ll•h·lor t:Jf' pr •. ·,:(•n :il j,.n toftephw. :\n' tt•phw •·rnplan·d to t IJ,. :-ot:t hwl':-T oft lw '1\dlinmm t"l'lltt•r was tlh· lilt·ratt·d. a!~•ng with T,.r!Ji,·.,ma la,·a tln\'" and d••nH'"• h~· I at t·r t•pi,.odt•s of cald~·ra <'• >ll<tJhl' and infillin~ by intraraldera Bandt•ht'T i~nimbritt· 1 :'\ielst•n and llult·n, l!lfi.ll.

ExJ,lnsiv<· t•r·upt ion!' an:! closd~ a,,,.,o .. iat('(t q1ida!'t ic Sl·diuwntat ion product•d l'~·du:al :<<'· q11t·nn•s of om• or mort.• pumil'(' falls, ,,ft<>n un· dt·rlain 1'.'" thin muclllow tlt-po::;its and oH•rlain hy t•it lwr ignimbritt• or thick pumin·.-•us mud­llows (Fig.:", I. Tht·:-w st•qtJl'Til"l's rt•llt•t"f indi\·id· t:al t·rupt iw· t•n>uts and an· SI'Jl<Iriltt'cl h\' intl'T· t-rupt ivt> dehri::; llow and hyp('r<'olh.'Pnt rated f1ot•d flow dt•posits I inrluding \"olnmir mud­Jl .. ws l. tlu\'ial "<>dinwnt!' (i.e. hraidt·d stn•am cnnglomeratt·s ). and deposits of ~lwetllt.•od ac­t i\'ity. Till' latter r~llt>ct high rat1·~ oi nggrada·

PROXIMAL MEDIAL DISTAL

Stream Flow

Debris . '"'•''"''·

:OWS yJ?t ..... ., ·swppolteO

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Dcb'IS FlOWS/ Stream Flow

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<vtr•nt

mo"oht,.olc.•g•c [:~;~~ij •ubrounGe<J

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Stream/~~~~ Debris Flf!l silearTi· Flow Mudflow

w•n•nu tr•c;troft

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Mudflows

Pumrce.f:'al

. ""e•t••o• '"htrs1.1rq•

no•m,ury graded

FiJ,.!. ~ •. C"';~:H.·ra!izf.ltl dt·pn~n j,rnal 't'1:flh·rh •·~ n·l.atf•d to indl\ icfual (').Pl··~J\"t .. t·rtJptton~ and intt-r ,•nJpt 1nnaJ phttN'' nl 't•ffHnc·n· tt-tfloll in pr•1Xitn;1!. n~··d1.r!..u1d di .. ~itl f'nn· Fnn11.t!1nn t·\)•·• .... lft' .. , .. , ••. 1••xt f,,, dt•l.ad:-- I

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I I

0

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0 . 5 km ... 1 .0 ll.m 0 . 5 km 2 . !> km .... E I

i~NI 0 Pumtce Fall

0 ~. sh Fall

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!=:::F•==t P3 I ::.+:==t:.=~-2_ .. ... ·-1' ..

'-I:==~Pt-- -aPt =-

20

10

6 5 4 3 2

Fil( . t1 . ('nmpusitt- tephro.str<ll igraphy of tht' Puyl! Form111 ion • hn11.·ill~ low~r . middlt· and uppN tephra grouJ• dl'J~•~il~ . prt'fix " P '' indi<"att•s a fan ·Wtclt- t·orrt•lat ion I st•e lt•xt ). ol hf'r unit~ art· l•l{'ali7.t'd I.'XJ~•sur~~ l'tlllfin•·U to ~P•~dfu· parts of I ht· l'uyt• fan (set- Fil( . I for Sl'<"lion ltx~ationsl. Other dt'>'il(natiun~ art' U:!:! and ('9=UJ!JX'r group rh~· .. litt• plinian dt'Jitl~it ~ iSN- tt•xtl. HA =basaltic a~h depo~ils. Jl<'mf= pumiceou~ mudllow dt·J"» •t~ . . "!F= Sant., Ff' (.;roup st·dinlt'nts . TF=-: ' l i H.a\'i rnrmKtu>n gra\'t'k Th!' Puye i1=nimbrit~ 1 :U,: I ' !1.1 :0.1u l ut approximately 4;, 111 i; a key strati.:n•phit:- nwrkl'r hurizoll in 1 h,.. fun .

tion that did not permit signiticant incision b_v fan drainage and werr commonly associatt>d with the formation of shallow hut widE-spread lakes.

Tephra deposits in tlw l'uyl· Formation :tn' in formally divided into t h n•e stratigraphic groups according to distinctive changes in th£' dominant juvenile clast t :.·rw. tlw Pn\'ironmen 1

of deposition , and susJWt't!'tl!->oun·es (Fig. li ). The lower tephra group t'ontains sevt-ral

widespread pumice fall deposits and thin ig · nimhrites. in addition to abundant redepositE'd •t-phra (Figs. 'iA.B ). ThPs<• deposits contain light colon•d, fibrous. hornhlt'udt•· and hitJtitt•·

ht•u ring ~h.\'odacite pumi<'<' and lt-sser amounts of dark gray or handc•d t wo -pyroxcm• dacite pumice 1 Tablt• 1 ).

A rniddlt• tl'phra grot:p consist s of a lit hi< -rich ignimbritt· 1 informally t·all< .. d tlw "l'uyt• ignit~1-britt>', dat<·d at :!.5 :\~0 . 1 Ma hy K/Ar analy~is of f('ldspar S<'parat<·s; Turht•,·ill<' and Self. 1988) and coarse-gmined Jmrni<·t• · flow depusits with largt• two-pyroXl'll<' dal'it e purnin• blocks that lack biotitl' and hornbll'ml<•. Associated with the ignimbrite st•qut'JH't• are St'\'t-ral t·oarst··. lit hie· ri ch pumin• falll" and fine -grained capping a!'h falls (Fig . ~) .

The upper t~:-phra group contains sc\'eral

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r

Weight '!1.

30 G15

35()

300

E 250

~

• • 200 • c: .¥ u

.c: 150 ... P6

100

-3 -2 -1 0

Md!i! -4 0 4

Grain Size¢

fil<( . 8. Pmfilt• thro11~h tht' "Puyl' ll<(nimbrite" and assodat.ed pumict' and ash fall~ Wi.: . 61 showinl! chanl!•·s 111 rnt·dian grain size CMdol and sorting <Jf depnsiL~ Ia o: \'alut·s derivt>d from cumulath·t! fri"QUl'n<·y c ·un·e~ in th•· ttrain silt' ran~t' -40 In 40) . and frt'qut!ncy ~·ariatio~n cul"·-.s of individual cnmpunent populati<Jn,; (fJUmice= ,;tipplc•d. lithi<"s .-·=;.haded, cry~ · tals = unshadt'd I. Samples tak!'n from homu~l'Ol'OUS ( ungrndt>d. massively heddl'd I portinns uf e•~t·h unit. Sh.•v.n at ri~ht are estimat.ed percentagt's nf accessory lithic types llbsel"•t'd in pumict' falls, P6 and,:; I[• (l ithic types rl'fer to Tahlt' 2 ).

thick rhyodacitic pumice falls, abundant lake­deposited pumice and ash (Fig. 7C), and thick sequences of water-lain basaltic a~ h. Exposures of indi\'idual units arP considernbly more re ­stricted than lower group deposits and differ markedly in mineralogy.lithic types, and grain­size characteristics. In add it ion. two rhyolite pumice falls in the upper part of the Puye fan (units G:2:2 and C9, Figs. 6. 7D) differ signifi­cantly from other Puye tephra units in compo­sition (Table ll , and are conjectured to have been dt·rived from sourcE' vents currently hur ­;ed benrath Valles II Caldera t Fig. I). Only ont­exposurP of each unit has been found , alt hou~h it is apparent from deposit charat' tt>ristics (spp

below) that t ht•y wen• orH'l' widt'!-opread plinian depos its .

Correlation of tephra units and deposit dispersal

Key st rnt igraphic t('p hra hori10ns were cor­related 1 Turbe\'ille, 198•)) using a combination of mineralogical chamcteristics, distinctive lit hie clasts, and t rat·e t>lt>ment compositions of large pumict- da::ts. Correlation wm; irnpedt>d in many cases by a highly \'ariable a:;semblage of juvcnilt- clast types in indi\'idual dt-po~its and hy the oft.;>n errntic lateral variability of indi­vidual tephra unit!' du<> to locnlizPd rt·working. The re!iults of tephra unit correlation are pre· sPnted scht>matically in Fig. fl .

Oft he 2!l primary felsic pyrocla.-t ic dt•posits t•:<post·d in tht> Pu:v-P Formation. Pirht pumice falls nnd two ignimhritl'" art· r<·•·nt.:ntzl'd fan ·

Fil(. ' und I

, I j ~ ; i ~

. ' I ' I •

Hey

• .. lldl)

3rey

• •• 1&11)

~ian grain '~" -4¢ to tded, crys · at right are 2) .

~posit

. were cor· mbination distinctive ositions of mpededin ~mblage of posits and .ty of1indi· reworking. mare pre·

ic deposits ~ht pumice ~nized fan·

'1 ! ' • • 0: • l I I 1

' ·""'~· . ' .... . , "" \~

.. '> .. \ TOLEDO\ EMBAY-.ENT

t '···· ··•; ./ .. .... ....,...Y .

.·•

A

., .. .. . , .

· ·,

Fi~ . 9 . l:.opleth maps showinl! di~JK'rsal patterns of pumiet' fnll T'4 based on the· maximum dinmett-rs (in C"m l of pumiC"t.> (A l 11nd lithic (Ji 1 clasts: \'ahlt's sh,.wuRrt> awrai(I'S ol !hi' fin·IMI(I'St clast~ lion~: dmwn~i"n) nwasun><l in outcn>p.

I I . ' ' I . I I I •. " • • ~ ••• , •• ~" I • • 1 J ) •• f' • ' d • I : I 1 • . - ' "" ' " • ~

•·· ,."*·,. · I

i•

I '1· I ~~ , .....

w I'

;. : it

I •

r

·.:·: ....

10

- 1!> E

I

• •

I

I

3

----to----·:

I I

' I

-3 -2 -, 0

Md p

0"0

Pumice Fall P4

-4 0 4

Grain Size~

F I}.: . !I! _. \ ' .Hh!~ j .. n II: J..:f .1111 :"'li't' \ har.ldt·rl~l :n· of l•llltlin• I all p.; t t: . J i \\It h d:-- !.tl:, I If urn { hh lllll.t I r .. , lau. Ullld : \1.uautaU1 ,, ,r'l ;~~ r .H: i .' ... t ·~ t ·c~t·d . ... -.-t · Fr~ .. l. st,, .. hn''" art· dtau~~, ·~ lllll:t·d:;,:l ~r,tll . '"''"' 1\l . i ·- • .oht ... 11rtH1 :.:, ,,; ,.., ,,,, dq;••:-.11~ Hnd trt•·J i! t'lh '\ rh .... ! ritn: : :•'f•"' ,.: , ·nmp• !llf•U1 P••p;lf.tl i. lll ... c :-.\"lrth~>l:- ,, .. u~ Fi~: ,.; , I ' :. a:,!LI! :l .t~ rt!:ht :--hn\\ .. J,t ·rt t ·llla,.'•· ~·~ • !,t:-.1 t~'J't·~

I Tal·-t· · ~I nh~· · nt·•! .... . tn · ,-~ ..... r~ !Hhh .. i:J urut P·1 .

widt• . :\t ll'a~t thirtt•t·nllnib tlult cannot ht•lat t • rall~· ~ · .,rn·l<~tt·d an· t•xpn,.pd in •lw sout lwrn port ion of tlw l'uye fan I Fig-. I I. two mort> in dw l'<l!'tt•rn f;t!1 ,.;t•gmt•nt,. . nnd yl.'t arwtht>r two in tlw northt-rn and prnximal expol'urt•:; lex ­

dudin;: two hh"··k ·atHi-a,.h pyroda:;tic !low ,.;e· qut· tH't·~: ,.;t·t· ht•l(l\\' I. In add it ion. pumit'(• and ;t,.h ••:t~titutt• a ~ir:nitit'ant proportionllfman.' t·pida,-r il' dt•pr.,,.;it ~ and lant,.;t rine H•dinwnt" i Fig. -:1.

Tht· limitt·d t'xpo,.:un· only pt·rntit~ approxi · mnt inn~ ,.j· <h·p,.,,.:it di,.)ll'r,.al,.; ha,.:t•d •.lll till' di,; -1 rihu1 ion of nr:1ximum da~t diamNl'i~ ( Fi~. !! I.

Tlw hi~hly irn·~11lar t hicknc·=-~ nuiat ion,.: of mn~t fnll depn,.;il:-< altngPt hc·r limit t ht• u:-:t•full· rw~~ nl r,npaclt nwp,. . Tlw contlltlr" f(lr 11nit I' I 1 F1g,; . ,;, 1111 :m•l• ·llwr 1'11n· tails di:-:play nudt· hut ,·nn~i,.;IPtH 1 n~nds. Tlwn• i:-: a :;~·i' t('mat il' t•a:-.t

and ""u! lwa"t di~pl·r,;tl. a!"" t 'llllltnon t" po,.l ·

1'11.\'t' .1\1\'F tt-phra dl'posit~ C \\'r!ght l't al.. 1 ~ ·,~q h 1. , · on~l~tt.•J:t with pmhahlt· so urn• n•nt,.;

in t ht• n·•rt lwa~t t'rtl Tschin •nta dome ('omplex. Abundant an·,., ,.ury lit hi,· dast:-: in tht'Si' pum· in· I alb I Tahlt· :!: Fig,.;, 1\. 10 I dn,.;t'l~· rest."mhiP T,..,·hil'oma Ia\ ;,,.. t•xpn,.;t•d t" tlw nnrt hwc:-:t I S('t•

I ,.j, '"' 1. wlwn·a, t hi' T,.;ch il'otua cll•po~tl :-:soul h ·

w··~l "' tl11· J;m 1 Fig . I J ;tn· :-<llffi;·it·nt lv dith•r ­

t'llt <'fllllJl""'t i"nalh from Pt1n• tt•phra,.; 1 David H roxt ulL pt'r,... ,..lllllllttn .. I H~:", 1 to ~·xd ude t ht'm

a·- pruhahlt· ,.,littl't'"· Tt phr:t di:-.p~r,.;al pattt-rn:" an· ;II,.., , . ,.ll,..l~ll·nt with pn,..,..ihl(' :'<llH<'I'>- in t lw

rt·J,:inn "' 1 ht· T"l1·do Emhaynwnt . Tin:-. Ol'pre"­"i•lll. hn\WH·r. ''lwtltt-r a l'.tlcll•rH or land,..!icl(• ,, ·art Fra"'l ' r c ;,,ff. pt•r,. . o'oltJ!ltltn .. J!lx:•: ~elf t•t .d .. Jn;-.f ; I . 1 nrt n\·d not !all• r 1 han :{.1\ \ Ia I ( ;arrl­lll·t el :t! .. !!,.,, ;,,;It''''"'' 11 .~. 111.~ . t.•arli1·r than

an~· l'\lrr<·ntly tbtt·d. ••xpn,..,·d P11yt · t<·phra . TIH· II· •rt h'' •··ll·nt l'ttn· fan t·:>.:pn,.t; n·,o 1 Fi)!>'.

! ~ < ( ..

<..: ... ~

c Q:

A

10·

~.

' ~1c a: 0 z 0 % u ' :0.: u o ; a: t,

r,:t-

Bi-Fil!~', mali. rh,·lir· Fr;r.ru: Ct,;\', J.,.,:in

~

•untain its and ;t l~llt''

et al.. vent::;

nplex. !pum­;emble st (see south · differ· (David le thefn at terns ;, in the depre!'· ndslide :Self et 1Gard·

.er than tra . ~s (Fi!!!'-

tOOO

100

• , c: 0 .c: u .II. u o tO a:

A

1000

~ 100 i 0 z 0 z: u ' "' u 0 oc 10

8

(

of~

TSCHICOMA FM DACITE LAVAS

0 UPPER PUH FM. RHYODACITE PUMICE

w Hb-RHYOOACITE LAVA CLAST IN B&A FLOW

• El RECHUELOS RHYOLITE LAVA

I ... ·-~ I

\~

I ~'"~ I . ' \ .L'

1 '. ! '_•/ ' ' I ' \ .! •

&• Rill Tt' 1 a La C• Sm lw Hf Tb Yb lv

1000

~ ;; c: 0 ~ u

100

~ 10 0 oc

c

U LOWER BANDELIER PLINIAN PUMICE

0 PUYE f!lo1 RHYOLITE PUMICE Cll

~ rUYE FM RHYOLITE PUMICE G22

• PRE-BANDELIER (SOC) IGNIMBRITE PUMICE

[J PUYE FM RHYODACITE PUMICE

B 8

.... ·«

Fig. II. Chundrite-normaliz..d ( Ha~kin et al., 1968; Thump~"" · I Yt!:.!) 1 rul'f' ·~l«-nwnt dia~rarn> t•omparin~ (A 1 Puyt' F11r · mal ion rhyodacite pumice~ ancl Tschicoma Ftlrnation darilt· Ja,·a,; 1B) l'u~·t- Format I• Ill uppN .:r•>UJI rhy•>dllrltt• pum1t·e. rhyr.011rite la\'a hlo,·h in pruxi::1al hlock ·and -a•h flnv.·~ (S(•t> 1_.:- xl ). and El Ht·l'hm•J,, Hh~·nlih- domt• hi\'~ ; anrl ICl Puye Formalinn rhynlitt• purnit'~">' If~:?:! . \9; Fi~ . fi1. Luwt>r Bandt'ilt-r plinian pumin·. pumin• from pn• -Bnndt-lit'r tSan IJii'J!n Canyon I ignimhrit.t•s. and ran~t' of Puy" Formation rh~·odal'ill· pumices. Tsrhil'•llna and El Ht·t·lnwln8 Hh~·.,lit l' data fmm

Lm·rfll'r ll!l!l41 and (;ardm·r t•t al. I t9fifil.

. l •. "t.~, .. ...

'I 1·. ; ' . . l 'i • . I i I • • I

I ..

:l ,, .,

t ~ , I~ I

! ~

r

I. ti 1 11n· clt-;trl~· proximal. Thi~ j,. ~ltPP••rlul ~~~­

the pn•sc•rH'I' of I II j!n·atN thit'klll•,..,.., .... and cJ\·erall ··oars('nt•:;s ·of purnin.· f;dl dt•po:<lls. t:.! 1

thick Rccumulat iuns of roar!'!!, lithic·du;ni · nat£'d pumkeous ignimhrit!.'s and a:.~h·rirh . d!.'·

bri:< nnw dl'JlO:<ils. ( ;l) a St.'ljlll' IH'l: of rwaJI.\· mono! i 1 hoiCJgic hlor k ·and ·ilsh !low d('po~it s 1 n t h(' uppPr part of! hf.' seci ion. and t ·I) ar; t.l\'t•r:tll fliHit'ity of :<Ill'('! 11ood clt-pn~its that domina!\ • int~->r·t•ruJlli•Hl st·qtlt'IH ' t'~ ;d .. ng thl' (':t~l: · rt! and ~·HJt bern port ion,.; o!tlw far. r Fu!. :,: \\'nn·:-<hark an,) Turlw\'ill<', in JHbs;. l'uye clt'ptJ:-its in tin:< area alsn intt>rlinJrer to sonw (·Xtl!nt with !-tJr · fan~ t~ :qw:;u rt's 11f Poh·adt·ra C rcJup lm·a ... and

1 a Ius hrl'ccias. relat ion,.:hips elst'wlwn: only cit• tl'<'ted in th£· suhsurfa,·e tGri~gs, 1964 l.

Am.Jt.site la\·n::: in tlw Tschit'oma n·ntt·r ex · hihit a fp!ted plaginda~E' · pyroxenl'~rnundnla:-.~

and phenonyst.s of plagiodast~. augill·. hyp£>r · l'them·. and magnetite r<;ardm·r l·t al.. J!li\til . Dacite and rhyodacite la\'as, on thl' ot lwr hand. are· t~·pically vitrophyric and c~.~ntnin tht· a;;.· sc·mblagl' hi · hhl·qtz-rpx·opx· mt, minor a pat ill• and zir<"on, and complexly zntwd plaginrla~t: glomNocryst~ with pronotmc<,d dist•quilihrium (sieve) textures (Loeffler. 191')4 ). !'uyt> For· mat ion rhyodacite pumi<"e deposits exhibit JWt · rographic features similar both to tht> older an· dt-sites and to the youngt'r, more e,·olved Ts<"hiroma hwas f :\1anlt•y, 197tl: Turht''·illc, 1986).

Figure 11 comparE's whole·rock tnH'e·elc· · ment. com posit ion~ of spq·ral Puyt> Format ion tt-phras with r11ck t~·pes rummc.n a~ PuyC' fall lit hies ( Tahle 2: Fi~ . I 0 l and with ot ht>r ,J :'\1\'F f.•ruptives of similar agt>. Puye Fqrmat ion rhyooa<"itE' pumices (Fig. 11 A 1 haw ~irnilar rompnsit inn~ to Tschiroma dacitt> and rhyo · dacite lavas dC'snibed hy Loeffler ( J9R4 I and by Baldririge and \'animan I 19RG). Horn · bl<•ndf'·rhvodacite law1 blocks in proximal hln<"k·and·a~h 11nw d(•p<lsits l;;.l'(' lll·lowl ar<· similar. rompnsit ionally. to l<'phra!' oft h(· up· per grt)llp (Fig. II B l . Fi1-rur<' II C shows c Ill~<' sirnilaritiPs ht·twc·en upper l'uyt' Fllrmation rhvlllitf' pumit 't' fall:-< ( ;'2:.? and C!t 1 FiJ.! . li 1 wn h

pumin· in Lat\' l'linn·JH· I pn· H:cttt!Pii•·r I ig nimhrt:1·s t·xpo~\'d ~out hwt·:-<t .. r \';cl it"' II <':tid. na 1 Turhf'\'illl• .'rHI :-;,.Jf, I ~tl-> .'-1 and J.,.w,·r Bandelit·r plinian pumi<'f'. rt>spt•rttvely.

In :-ur1mar~·. t lw l'un· allll\·ial :an pr•JhabJ.·; n•pn•..;t•nt s onl.\' a small prnport ion oft lw Ill a · t c•rial t h:tt rna_,. t'' mr .. i\ ·ahi~· haq· I •tTll t·rupt•.•d t·xp!.,:-in · :~· fn•m t !11• Ts<'hirom:• and El Ht· ··huc•lco~ donH·~ . <·r frc•lll q•nt.• t lwt "···n· oblilt·r · ;ctt·d hy t ullap,.:t· ,,(' tf ,t· \ 'alks caldt: r .• ,.. . It i:- liil ficult t• ~stimat<• the ,-.,:unll' 111' juvt·nih· pvrodast ic matPrial pn•servC'd in t lw fan or t lw pl'r<'t•ntagl·:- of th<•st• tl·phra:- dNi\C·d from in · di\·idual lm·a dt~nw,.: . llt>W('\'I'f. t lw primary dl' ·

posits and n•cogniwhlt• \'fiiJltiot; ,.:c·qut•rt('l'l' sugj!ht 1 hat n minimum of ftftt·t·n :-mall I 0.1-1 .0 krn 'l t•:q>losiH· t·rllpt ion,.: an·ompanit.'d t ht· growt iJ 11!' la\·a donws in tIll' nort IH'a:-<tl·rn part oft he Tschicoma \'llkanir t't•nll•r. in add it ion t•' tw•> ~ignilirant t•pisorh .. s qfntkattian art i\· it~·

probahl~· ass•ll'iatc•d with gr;l\'it ·H•"nal la\'a dcmH· l'llllapsl•. Abo, nt ka:<t t hn·t· l'XplosiV\' t•rupt iuns po~sihl~· assoriatl'd with t l11· \'oungt·r El HtodHI<·los Hh~·olilf• dnmt·!' ( J..,Pfllt•r t•t a!.. HI~~ l art• H'Jlrt'sl•ntP<l. as Wt!ll a~ two plinian dt•posits from soun·e~ now burit•rliH'tll'ill h Vallt'l' II Caldt>ra. All of this aC't ivity occurn·d ltet wt•t-n about :u:, and 1.!) M11 (l\1anley. l!lif), 19';!1; Turlw\'iliP. I !I~() l.

Charactcristks of pyroclastic and associated deposils

PumicP fall clt·posit:- in tlw l'uyt· fan \·ary from lit hic ·plltlr pumit•t• and a~h falls 1 Ftg. 10 l to · · r~·st;d and lithir·domlltall·d r·all dc·posits with only ~ulmrdinatto nm.,unt~ of pumic(• lc.f .. Fi~ .

~.fall unit l'f.i l. Tht•s£> ft-'aturPs an• di~tinrtiw nf fall!" produr£•d h~· :-;uh -plinian and \ ukanian t•rupt illn~ . n•sJH·I't i\'!'l:v I c .f.. :\1·whall and :\It· I· .._,,n, J~IS:l; HPikt•n and \\'nhlt·tz . 1!1>'-;' t. and Sllj..: ·

)!t'SI t bat hot b t ~-))('!"of t'ntpl inn C'PtniTlOnJ~· :lf ·

,· .. mpanit•d t lw gruwt h of '(',.:dti•·nnw l:l,·a

dnnw,.: In :ulditi"ll. Ill"'' l'un· lalJ, nontain a

.I

t:on·

wid C' (•s,

trt>t : thn I 'Ont

lain

l!{ ·

tid-

bly na· ot.ed Re­tE'r· dif­ni\1:' the in·

· de· :lCeS

0.1-: the part tion ivity lava >sive nger t a\., nian ·aile!\

ween 1979;

'ts

· from Ol to , with · .• Figr

nctive ·anian i Mel· 1d sug· 1ly ac · t lava ttain a

B

3.0

2.0

"Q

6

1.0

A

PVG

P4 ,­(

I / / /

// / / / //

I / / I 1 I

I I I

y

, 2 4 a PS // I \ I ' .,

\ '--~ /

----

P7

\ ' ' / ', ', '-... P3 __ ,.. .,,.. ' ' '-:...---- - / ' ...... ....,-----~ ........... / .................. ___ .-.-.---....... -----'--~~ --- /

-- _____ .....

-4 -3 -2 -1 0 2 3 Mel 11

:lHI

Fi!! . 12. A. Ternarv pr•.lJHlr1 i•ln~ •>I h!lhl mlvr.,d hnrnhlendf.' ·J1UIIlln· tl.l' l. durk l!ra~· :! ·pyn•xt•IJ(' pumir•: UH' I. und aphyrk, JHHlrl~· Vl'~ic:ular ibloC"ky I ju,enil<· rla;ts ( P\'G I in l'nlption st-qw: tU:I'" 1'1 ·1':1. 1'~ · 1':"•. and Pli·l'·; l»t·!' Fi.:. li and text fur detail>l; halrhf'd fields indudt• all sump I<'~ analyu·d from ead1 ~<'(! · wnc·e Itt:. :!4 1. H. r.tf.'dtan grain size I Mdc 1 plottf.'d u~ain>t Inman's t HI~>:! 1 surt in~ JlllrDJntc>trr 111 Cd tint hc• ~ani!' I • phra !'('CJlll'llfl'~ a!' in A; c·onr.oured fields art' Walker's ( 19~:11 rot'rl'entagt'l' of pyroda't i<' fa I: dt·posic,. ~~ uditcd wnrhh• id1• .

wid(• assort :nent of distinctive juwnil~ and nc­t'e!;sory clast t~·pl's (Table 2 i, and an overall trend is apparent stratigraphically. At least three consecut i\ e s1.•quencP;; in the I•Jwer group rontain pum!n· fall:' I Pl. 1'-1. Jl(); Fig. HJ nwr· lain by i~nimhriH· . Eilc·h "t'quenn· (•xhihit;,

(•tlllC.'r an upward incn•a!:l' in tlw proportion of d;~rk gray or handPd pumice in successive fall deposit!' or changt':- in tht• pro port ion!\ of poorly \·o·sicular ju\·(•nilP mall·rial and pumiceou!' ar­<'•: ,..~•>ry cla!'t" 1 Fig. 1 :!A J. Thl' apparPnt c~·clit·· it~ · i,..a) .. ., n•flt••·tt·rl hy l!r:tin ·sil.f' clat;1 from ho·

!· , i t i \ •

i l ,. r

A

8

E u 1l>O

• • • c ~

!!tOO .t; ...

50

2 3

D t! b r is· t I ow

6 5

E ~ . e ~;

41 I

\ I

I

I I

... )( E < I

t 3 I t

/I I Mdo G"Cl \

'/

.. ~ 0 < 2 I

I

I • ... )( 0 < "Wet" A a'>

Debris Flow

-3 -2 -1 0

Md 0

2 3

Debris Flow

• •• •· l • • • .;.~

tJO oO OC oe•ooao :·: ~ g ~~ ··~Q ..... E!--)(~--- < :·~g-gg.g I Unit 2 :g~.~g: I ~ 0 C\,o o 0

;·~: ~~; I Unit I' Mdo

oe ' )( ''a< J.-.r,....,..-m Red Clay

~~:...=.f

~~~:"::· Debris Flow

-3 -2 -1 0

Md ~

30

20 01.:> c k y

10

~I 30

20

10 (.) Unit

(1)

c (1) Fibrous > Qtz-:::3

K a par ..., 10 Pumice

-4 0 4

Grain Size 0

Weight '-

30

20

10

30

20

10

30

20

10

-4 0 4

Grain Size0

Gray Aphanitic Dacite

Blocky

~ ~~ -r-~

: ~~ Grey <' Biack :,..::.·~: · Basaltic . ,,, .

, ., ·• llndealte

50~

Fibrous

85'-

Glass

Gray Tuba Pumice

75'-

Hyd . Alt. Scoria

Red , Gray Basaltic Andesite

70'\,

I i

<'<

S<

h.

SJ ic .

\\';

E'll

Th tio

hj!. t,f,.,

lowt · da,, ll 1• . :Uf ·f· ·

,..,,11:

..

H

be

r

te

tnll;:l'llt•mt,.. : i.o·. llll;.!f<Hll'd . m;,,. ... i,•·l~ IH ·olol, d 1 p:trl" olt·a.-1, I all unit 1 Fi;.:. l:!H 1. l'11111in· tall­·'' Jilt' ha>'t' od t•:tch "'''llll'llt't• iiJlJlt•:n·to ht · "'"d o•ratt:ly Wl:'li :;orlt:•d and rich in < ' r~·slals 11nd highl_v n·:-:iculnr· hhl-hi-h(•aring Jllllllin· . 0\(•r Jving unit,.: an ... prtl).:r• -,..,..jq-1\- l)(~ll(•r ,.,rtt·d. ,.,.

pt•ci;tll~- 1'7 i hat ""''' lwl'nt!t(•,.: lllltl'!l firwr­gr;titwrl :md ridwr rn tl<~ll · \· .. ,_irubrr ·~l:t,..,.. _

Tlu·;.t• 1 rt>nd!- "'';.:!!t' "'' :'IH'n•s,;i,·o·l,· hi;.:ht·r w:llt'r , -.. nto-nt,.. int•r!!pt,,.n,·n!ttntn,.._th:tt t'~tttlo!

ha,-,. initiatt•d pr,•tn<lttHf' dq,n:-:itinn .. r finn ;_:r;titwd nt•ll• ·rial and ,,-.,,J!d han· dranwlicalh lolWt·n•d erupt inn rnhmtnlwight;. 1 \\'alkl'r. l!J." I ; H. llnu).!lllllll. pt•r,... ,·.,mmun .. l!J~:-. J. ('llllllllllll

1 f<tlbll ion:- lH·I Wt't'll phn•:tlomagmat ic and pn·­clomi n:111tly nw).!nwr it· acr i' it .\' h:t\'t' ht·t·n do<'· tlllH'tlted I'Tillll dlllll(· <·r•Jpl inn . .; l'l,;,·wht·n· I llt·i ­kt•n and \\'ohlet z. J!!s"; I. The,_,. d:ll a: howt·\·t·r.

d''"' 11 sup:l•>rl tlw :'lllo!J.:l•:'t inn I hat phn·at omag · mat ic act i,·rty rwt'fl alwa~· ,.. hl' JHt•cttr:-nr~· to tnagmat ic t>rupl ion:- fwrn ).:rowing dnm<·:o: . In ;tddit i; Ill. i r :-uh;;t'(llll.'lll t:-rllpl itlll:-' had lappl'd tkt'Jlt•r. mort· \olat il<·-poor t:l:t)!lll:i, I ht' re,;ult · i 11 g l ' rupl io 11 pl u IIH'~ would al:-;o ha \'l' hh·n lO\n·r ;mci It'"" t·lft•t ·ti\t' in cli,.,Jlt'r;;ing cnar,t• da,.t:­, Carey and Sparks. EJHii l. Consl·quent cultrmn ····llap:-to or a,;h tinrnt;;ining t:-\parh ann \\'il­,;on. W76: ~park:'t>l aL 197K: Horn. I!JI'iti 1 might he expected to haw prodta-t•d thin hut wirh· ­,;prf'ad pywda:-tic tlow,; ill,..l• rich in P•"•rl:-· 't·:- ­icular juwnil(' gla,;!'. Hnd Ja,·a lithic:-;.

l'umice dt·P''"it:-: are rnon· rl''"i·l_,. ,;pat·t•d to­ward tht• top o:f till' lnwt•r ll'phra gr .. up. :"IIJ.:·

)!t·sting that t>xplo~ivo· ilt'll''it~· ma~· hil\t' ht·t·ll a<Tt'·leralecl duri Ill! 1 hi,; pc·rind.wlminat ing with <·mplarement of tiH• l'nv<· ign;r!rltritt• 1 Fig. ti 1.

This pnssihlc· incn•a,;t• in tlw frt•qru ·nt·\· .. r erup ·

1 ion" i,; al:<:o n·tlt•l'lt·d lty ''"""l'iatt·d t:'pid;;:-1 i, ·

.· .... .

,j, I'"" it .-: I hick intt·r·t'riiJ.•l i"ll "''l(lwrtn·,; of

ltit ,dllo\\'" •H 't·orr and sltt·t•lflo.,d dt'JI'" ·''· ;tiJIJII

thnr in "' ·q1wnn·:- ht·low.lu·!'flllll' lr•,..,; appan·nt

I'JlWilrd. Al,;u, <il-bri,; 11ow Gl'po:-it:- IJI'comt· t hickl'r 11pward intlw iitn and pn•dflllllll:llt· <J\'I'T

rla,.t·pouor nnuhltt\\'"· Tht ·,;t· tn ·rub r~·llt-1'1 in ­crt·ast·:- in ""ttrn· an·a Tl'lit·f and pro~: irnal fan

"'"lit' and ,.,;gut· ... l :111 ir.t'rt·as! · in till' :tlll•ttlnt of "' •arst· \' ,f,·;tll id.t,..l il' lll:ti o-rin) a\·ni l:thlt· I • • I )J, .... ,.

n .. -.,· •.. :\:-- '''"' 1-.y talu,. ,..; 'Jl' '" an· virr •r.dlv uhiq­!Jil:•u,.. !'t •aturo·:- of ntlo·:lllic donu·,; : \\'ilriarn,.._ J:r:t!: Hn~t·. i!Jl\'; I. an incn·: t~t· inthP !rl'qiH'Ilt'Y

otl (•xp! .. :-il·r· ··rupl ion:-: fro1111 Ts.-hi<"oma dornt•,; 1 1111~1 lwn· gn•atl_,. an·l'lt•rato·d l}w llJo\ t··nwnt ol J;, rgl' ,., ,Jo Ifill':- of po"rl_v con,..olidatt·d nt:ll !'rial. proximal!_,. n ·pn•,.t'Jift·d II:-· \t•ry \'ttar,.. .. grairwcl dvhris <1\·alandws and block and -ash pvroda!-­tu· !low,.., and di,;lall:-· lr~- !'tackt·rl. dast -sup­P• •r{(•d dt•bris !low d('po,;it::; I Fig. !11.

l'pper IPphra group pumin· falb ;ll't· ··nmpar­ariH:>l_,. thil'k wlwr<• pn•st'r\'l·d tl·~ rnl in ('X·

Jl""''ff'" up to :20 km fr11111 so11rn•. l>t'Jl""its an• ln·qw•ntlv w:rtt·r -lain and fl'W•lrkc.·d in di,.tal t·Xp••sun·s 1 Fig. 'iT l. ,..uggt·sting an int' rt.•ast' in liuvial activit~· and lnkt' dt·VI'loplllt'lll ;t)nng tilt' tan lilt' as I he Puyt• fan nHH•.m ·d (Fig. '{ J. Th{',;t• 1alh- t'ont a in a vari<·ty of cognatt• and acct·"sory lit hie typt•s not ohsNwd in t ht> lowt•r group -nlt,;idiun. a pat ilt··lwaring·handPd p111nin•. and a '' idt· a:-~ortuwnt of highly purphyrit it.' rhyoda ­rit ic d;l,.ts - and <H'compan:-· an app.tr-:nl up­ward int'Tl':tst· in 1 lw prnport ion:-; of qWtrt z . and ,anidirH·-ph_nic lava da,..t,; in t•pil'ill"lit· ,;('­

qoa·nn~:- I Fig. 4B I. l'umict• lapilli intlu·;IJrl;llls ab" t{'ncl to I)(• rnon• aph~·ric. and till· Jtt·n·t--nt­

a.:t· qf dark gray :2-,p:-·mxt•nt· pumit'f' t·vidt•nt in lnw~· r )!roup dt·posit,.; dimini~lws 11pward 1 hr"ul!h rlw uppt·r j!roup,.._ as d.,<.,. I lrP pr~tpor-

FJg. I : ~ . :\ . ( ;r .. u: '-ill· · .... olrfiH~ pr·di:,. r hr·•:;J.!h 'iJ'p• ·f l't:·.;, r. •fll;.tt 1· ·11 rh~· :d i h · J'1olll1"f • f.lll ( ;~ . ~ t '"t' Ft;..: fi • : nun,1wr ... i.tl fiJ.!}U

"f ,···,bunu rPh·r 1•: llidt •. idu:d fall \l!\11 .. • ... , till,"! .. .... 111Ft;.: ...... ' ))l .t ::r..;n ... •tl nd11 ~1\t· tu·rn:ttl:ll.~t·:-- 111 Jll\t·nal • . • !,, ... 1 '~· Jtt·~ 1n

;. •'•\"t·r and !lPP•·r :,,: I :.all; ... and l ,,,_. 1!\ t·roti! P'"l '"rr I• •It:-- ' t l , ,, \., .... :--• •r :. J it hu I\ 1 w:--. . 11• •It· t l.o~t 1 ht·r•· art rl" ( • 'rrt·:--1•• •!1dU1~ lit hu da~t IYJlP~ 1 it· 'Lff,j,_. :.:.· I Ill P&:\t' F·•rnt:·tt 111n l.nJI.:l~~nh • r . ll h dt•po"'lf ..

li . Pr.,(iit· thr"~:d : •=pp..:· I'··~·· · h ·r:n.t: IOifl rt:\ .. !;· .. f'·UHI• ,. f.rll c ·~ , • Fn: .... , . ·.·1 1' o~ud 1wn t·nl.u:• · ..... t ( b :- 1 1 \'1'''' . ,1. .. ,·!"\ t·cl ,, ... ·h , .•. ,:-.,,r': !Jt tnc-. 1.11 hh 'J.t ... r T qtt· ... f r••fll ho~t h f ' ~ ~~ .uui f If .tr• · .... n, o~ l.,r 1• .· l:t\ ;, ht hu! .. .:u ·:· n ·p: 'r1• ·d ! r11fl1 rlu · I '.tit::. 1 ·.,ny"n f-", ·r::1.11 j , 111 f · \1•• 1 .... ,.,! ... . 1: j ! t; .• ::d \\' ... • •of ) .tJj, .... II• .• !dt ·r .. 1 t •.trd:~t r, 1 .1: . 1 ~"' . :

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11"1 1 11! hl., .. k, . ;..:l<t.•,.., llo;tteri;d, In :u!dtt i""· lilt' dt'l"'~ll:- ;lrt' ~··lll'T ' dh· lithil'-p••"r and t"lllllll:lr all'- !'!y t'll ri.-lwd in fn·t · l'f\ · ~t ab rl.'!at i' t' to lll : i 1,..

below. The,-,· tcaturt.'~ liUgge,..t marked rhangt•s in tilt.' n:!l: lrt' .. r f'XpJ,,..iq· t•rupt ion:- . that pr .. h· ;Jhh , .. . ,.,llllpanit·ol ,·iJ;n l;.: t·,.. in 111 ;1p11a ro1np• ·~i · 1 ion c ;lnd rht•"l"~' 1 in tlw T,.l'hinllll:t ,-olcani,· ··c·ntt·r 1 H;tldnd;..:t-- and \'nnirnan . 1!1-"ti I. ,·.,in cidt•n' wi:h t · X!~!l-inn .,f till' El H•:dllll'ic·-l:h, · ••Ill<' dll_lllt'" tJ,,u •ltlt·r .-! al.. l!h~l Silit·i·· It· p!1r;1 ol, ·po,..it,.. 111 tl:t · l'un· F••rm<ttion ;wr,_i,..; up"· a rd t" tlw I '!t·t'l "' l'IH' t•rc ,,..i1111 ,..urfiin· ( Fi;: . ;; I. , . .,n,..idt ·rt•d t,,. \\':t rt•,..lJal'k 1. 1 !lSti l In rt'IHt ' ,..,•nt ••r.h· tn'nnr ,.,..,·;~rptllt'llt rl'ln•at prior '" t · mpL~tTillt'lll "' t !It' Lnwt•r Handt•lit•r '1 \ tff ap · 1HtlXintatt•Jy 1.-Ft :'\Ia .

~,., t.•ra I ha,;;dt w ph n·<~t oma~nwt ic I' rill~~ i"n" .,,·ntrrt·d d11nn;.: tlw dq1n,;it i11n ,;fan upper l'uyt' lat'''"' rint· ""IJlll' llt'P t Fig,;.:!_ fi: al:-;o "Cult·hra" bkl' ,·1:-.y ,,f 1-\t·!lt•\·. I ~i:,,; l. Tlw,.:t· unit,.. intt·rlin-

·::••r with P11.n' tltt\·ial gr;l\" £•1~ anci lakf' !<t'di ­lllt'llt,. in t lw ""'" IH.-rll port i1111 nt t lw !'a 11. and rt·fit•l'l t lw do:'t' """"'·iat i11n ofT:-d1ict;mn- Plt\'(' ,-.. dinwnt;llinn and phn•atomagmatic ncti\'it _v in tht Ct·rrn:- <h·l Hio , -,,Jnmil' fwld t Fi:-;lwr t't al .. I !IS-1 1. C11:tr:-;t·· dt>hri" tlnw depo,;it,.. domina\ e t lw upper l'un· Fnrmatit~r: innwdial ;ltHldi,.tal fan :-l'~mt•nt,;. and art• t'\"t·r.nvlwr<• a~liori:tt!'d with pumin·•HJ" l11l\ial and lacu:-trine dc·po~it:-1 \\ 'an~;;hack and Tur!wdllt•. in pre,.::-; i. again ,..ugge,.tin:.: tlw imp•lTlilt1l'l' ,.f ma;;:- tlow pro ­Ct·~>'•. '' 1 alnn)! ,,·j: h (\·rr• '" dc•l H i•l ha,.:CIIt ic t'rtlp ­

ti"n~ 1 i!l inl11a·n•·in;.: !neal drainagp paltt'fll"' ­\lall'' "' tht• m!!dllnl\'" nnd dt"ltri,.: now" 1\"(•tt•

t•mpbt HI :-ubaqllt>•.HI:"I\ 1 \\'an·,;hnl'k. 19~fl I and ,·;111 lw rran•d 1:pf;1n t•> lateral),- f'qui, ·alt•nt

pr· ··xim;d hlnck-;IJHl -a,-1; "C'tj\lt:nn·:-<.

HJ:\·,, I:t• · 111111: in· Ltll .' nn ur in t,,.,, lln·a,.. at

th·t · •p "' tht• I'll\·,. tan :llld art· hnth ow·rlain h,, ~ - 1 m "' l'pid;t:-1 i· · nwtt·rial f unit,; C:2:.! and (' :1. Fig. li 1. Tht·,t· ;tn• di .~t inr: from ot lwr Pun• tt•phr:l,.:. alth•n::.:lr tht·lirnitl'd t.'XJln"un· ot'Pa.-!1 rt'll•lt-:·, 1 iwir ··nrr •. ·l;tt i"11 ditfi, ·t llt. \"nit I;~:.! : ,.

1:.!" '"'thick ;IIHII'"II'-'1:-t,. nl ,.j:~, lallttnll,...t·;u·h :-;l'l •:l rillt •d hy tt.f-. :l.flt'lllCJt'lt'r\· lilll', cry;;tal-riC'\1 1

a,..h tFig. 1:1:\ I. Thi: dt•p••sit ('Otltain:-; distinr tin> apl;)·ric tuhl· (capillary) pumil'<~ with vesi­

dt·" of a~pt·•·t ratio -I O(l: I . Thi!' juwnilr da:-<t t."l"" 11 . 1~ nnl~· ht·t·n ,,IJ,..pn·•·d ,.j,_,.,,·Jwn· in tht· : m · I tmdl'i it·r :-;an I>ic;.:o ( · an\·on il!ll i !II h ri a•s • .n t l: t· ,..nut h\\·t•,..tt•rn m; ,r;..:in ••I \"all• ·:- il ( 'aldt•r;c 1 T urtl"\·illt· ;llld :-it·IL ;n pn-,.. ,.; 1

1 ·.1pp111;.: tIll' l'uyt· Fnnnat i1111 it, t ht• ··•:nt ral p<~rt i1111. ,f t lw f;n: j,.. ;1 "' ··nnrltlnit (( ~!l. Fig:-. 1;,

';'II i. a :.!;'•ll ·t·m ·thit·k rlt~nlttt• pumin• fall n•:-t ­in~ ••II a di,..t i n•·t in· r··ddi~h da~· hnrizon. Si 1 ky whi:t·. "anitlim· · ph~· ril' pumin· in thi:- dt~posit is dH· mirall~- and lllOTI•h"l"l!il'a)l_, indist in~ui,..h · ahlt· fr••m pumin• t•f tlw l.~twt•r Bandl•lic·r f(illa_it• l !'liniarr •lt·posit:- I Fig. IICI that o\'t'r ­lif' tlw l'u~· ~· Furrnatil•n in thi!' an•a . l'nit ('Hi~ cii~tll1!-'11islwd from tlw <:ua_il' p•unin• fall h~· a hi~h matrix da~- t•ont t•nt. ahsPJH I' of as,.:ociat t•d igni1nhriH•. o\·Prall finc•r grain ,jz<· and hrttt•r s11rt in~. and <Ill an••malou:-1_,. n~·:-ta1-t•nridwd lnwt•r fall unit 1 Fig. I : H~ i . Thl' ah,;t•JH'l' oft ulw pumin• and dJ<•mic-al drs,.imilaritit•s di;;lin -1-TUi:-<h tlw unit from pumir•· fall ( :~:! (Fig. IIC l. altiWllJ!h hot h llllit,.: :'IIJ!J.:l'Sl t'll11l('lll)l0nlnl'ity hc·t wc·rn t'Tilpt ion,; I rom t hl' T "' hil'oma/EI Ht· ­chuelo,; clomP" ami rh:volit ic iglllmhrite-form ­ing e,·c·nt" in t ht• n•rll ra 1.1 i\ 1\' F ( Turh<•,·ille and :-i~· 11. J !I~K I.

Two thin i~nimlmt ~'" I Fi)!. li I in t h<• lowl'r tt ·phra group o•.-rur ht·t wt•<·n ~·oarst•-grairwd. lit hi·· ri. ·h pumice tall:- and art• t·omposf.>d pn•­dnmitwntly of grav ~-p~· roxt•m• pumi<'E:'. Tlw i;.:nirnhritt•,.. l' <h:· !J I"Oll,..j,.:( of a rdat in•Jy hollltl· gt'ltl.' llll~ main n .. w 11!1 it a ntl Sl'\' t ' ra I ti rwly "t fill ­ifil'r.l. fin<·· '" ro:lr,..t· -grainl'clll\llllit·('o\1!' layt•r..: th:1t ,- ,u~· lrorn lithic -ril'l1 tnlitltil' ·poor and t•X · hiln1 ,.;light pinch-and ·!'\\'l'll ft·ntnrt>:-. oftt•fl with thin inH·rn·ning a~h lity1·r,.. f Fig. 1 ·lA l. Tht•,;t•

i).! n t rnbrit ~'"a rl:' :-lin i lar to dt'P''"''" all rihut Pd t 11

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....... ......... ... . PUYE [~I~ Pumice-Flow

IGNIMBRITE ~~o., Lithic-rich ··• Main Flow Unit

DAsh-Fall

~Pumice Fall

D lak e/Fiuvial Sediments

Clay-rich · Debris Flows

Fig. I '•- Faci~~ \'l!riat >~>ns ,,f tlw l'uyt> ignimbrit~ '"'·'~ al~o Fil(. ~I; not!' t>~pt•dally tlw hllt-ral varialtilit~· of a~~·lt'JIII•·d pumi<'t· flows and fall <lt·p·•~it~. <Jnd we,tw..rd tran•it ion of muin tlow unit dut•to suhaqut•"u~ t>mplanmwnt. Cla~t siz('~ not to ~t"alt·.

highly energetic flow regimes (")ow-aspect ra· tio ignimbrites"' of Walhr et al.. l9hO; Walker, 198:>: Wilson. l HH4 i. Both units exhibit consid­erable lateral ntriability within relatively short dist.ancPs. and in proximal expo!Oures are much coarser-grained, massively hc·dded. and morf' lithic·rich than di~tal l'411ivalents.

The Pu:w ignimbritt•oft he middlt•group also exhihitl' rnn,;iderahle lateral variability yet is consistentl_v represented in diffl:'rent exposures by a :,! .. :}-m-thirk. wry lithic-rich main flow unit (Fig. I;)). l: nderlying deposits vary fromroarse. lit hie- rich lw!'.ai pumice falls 1 Fig. ~I to v£>ry coarse. clast·supported pumice·f1ow df'posit;;. The main 11ow unit is Hon-welcled and con wins a variE-t ~· of largt· t > ·lfl em diam. J. an:rular to

sub-angular lit hie l'lasts of Tschirnma Forma­tion andesite and dacite lavas CFig. 14B) ~ith small rounded pumice,; in a matrix of pink ash. This unit has a sharp basal cont!U't with under­lying pumice dt>posits, hut a gradational upper contact with thl" overlying pumict' flows. Th(• Pntire sequem·p attains a maximum thickness of about 10m in channels I Fig. If) I. The Pu:.<· pumice flows. and a thick seqm•nc1· of largely reworked, c·oarse-grained pumict•ous deposits immediate)~· he low tlw ignimbrite' 1 "t1lder pum­iee-llow!-". Fig. (j I, vmy from matrix-supported to pumiceous clast -supported and c·ontain large 'up to 70 em diam.l, wl'll·rounded. hreadrrust · like pumice hh.~<·h·- t Fi~.:. 14C) in t'XlHJsurt•s !."1 :!0 krn from soun·l'.

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T\\t~ till< k IJ!"d' ;,nd·:hli t1ow "l'IJlH·Ill't'" '" nil 111 t ht· pnoxun:tl li(IJlt·r l'uy1· Fornwtlllll ( FiJ!s. fl. ti 1. Tfw>'t· ""qut·llC:l·s on· informdly dt•,..ign:Ht•cltlw E..;pai1<Jia and ~Hnta Clara block­and-a.;h dquo,..il.'. Th,·.\ ditlt·r in <aJ>JH·arann· and th·p• '"it da;J rac-t t•ri!'t ic:-;. Till' Espanola !'l'tjUt·lll'(· •~ 1;-, 111 1 hit'k anti •·nr; ... ist~ of at lea:-;t six flo\\

nn its di,..r i n:.:ni:-lwd h\· s\·mr:wt rica! and rt•\'!•rst· ).:radi ng of l:l l').!t ·. :-arhal\).!'llhr l;l\·a da:-;t ,;. A llunit,..

art'lltlll-WI·!dt·c!.lnrt ~tr••n,.:!~ lithifit•n. ann j.!Tlldl'

latl'rall~· and \'t•rtu·all,\· to n•ry t·oar,..•.'. pol,\·lit hnlo~ic rlebrj,.. flow dt•posits with prr­donunantl.> n·d and gra\ porphyririt· dal'il•· hnulch•r,.. t ""nit' · :1 Ill d1a111.1 in an induratt·d pink ash matrix.

Thl' o\·•·rlyi ng Santa ( 'l<•ra st•qut·nc<' cor,t:a! ns

J:~.;-, 111 ot \\'hiH·. aim""' monolithnlr>gir hlock­and-a:-;h ckposit,.; with :-ix unit~ sPparatf'd by thiniH,\'I'r" ot tlu\·iall\· n•workPd Hsh. Thu;t• dt·­

po~i~,; an· dist i ngtri:-'llf'd frcm1 t lw underlying

J-:,..paiJola ;;pqu<·lH'(' by tht> poor)~· ronsolidatt>d nat llfl' oft ht> fornt('r. t ht· ovt>rall white ('Olor. a mono! it lltllogir hornbll·rHh·- rhyodacite bould1•r as:-;(·mblagt· t ~t·P Fig. 11 B J. and n comparat ivt.'ly

high rat itJ nf matrix a,;h to subroundt.>d blocks

i Fig. l-tD r. Th(· flu\·ially n·workc-d ash lay('r~

do nut contain abundant detrital material. sug­gesting fairly rapid t•rnpiHrf'ment of suctessi\'l• flow units.

Discussion: <•ruptions from Ja,·a domes und e\'olut ion oft ht> Pu~ <.'Fan

:\lost Pll,\'l' Formation l:'ruption sequenn.•s ~ugge~t tnm~it ions between phreatomagmatic and pred,Jminantly maj!nuHir (suhplinian nnd plinian 1 art i\·it~·. !-imilar to lava dome t•rup­

t ions doCllllH~ntPd (·bt·wht•rl.' 1 Heikl'n and

\\"oh lt>t 7.. 1 !I~ 7). Pumice falls oft he lower group

rCJrely E'Xt't>t'd '2m thickrws:-: (e\'en in proximal t•xpnsun•s ). and eomrllfmly t·xhihit highly t·r­ratir variahilit~· in grHin sizt•. sorting and clt•­posit grading. suggt-sting fallout from low, rap­idly fluct ua1 ing NUpt ion columns rat ht•r than from ,;ustairl\'cl phrml:'s. Fall deposits an• gt·ll· t~rally poor!\· ~ortPc! part ictJiarlv in ha:-;al tall

tilt~ I,.., a• ·,.,._,Ill;! t11 till' pn·rn;ttttn· tl•I-Lint! nf:1,h

lrtlln \\';tl•·r·rich columns. TIH·,..t·unit~· :~J,onll: lain ah•lllc!ant po!Jrly \'l•si!'ular juv1•nilt· matt•· rial po,..:-ihl\· forrrwd b,\' qll('lll'hing or magnws I •r 111r I • • ·, t·-wtt !:tt ion. )'}u·n: ot·r\·:-t !-- 1_\'j•ll'il ll_v d j,.. J•lm·t·\ i.!t·nn· o! i n.-o:nph·t t· di.;:tggr!·g:•t 1on fro111 f,o,..t pumin gla,.,,.._ and lilwrat!'d rn·•tals oft<·n

h:t\'1' a I: 1 r~•- po-rt·<'n t a~f' nf ~· Ia~" ad h1·ri n ·~ 1 o t lwi r ;-.tJrt',:n·-. 't:ggt·,..ting im·lfi,·if.·Jtt magn.<~t;c lr:tg­r:H·nt at ion and possibly lt:'-'s ,•xpllo,..in· 1 rup lit,ns (:\k~H. 1~17:!1. lfi~hly porph:-ritil' cog­

mill' lit l11n:. ,·ar:ving from dt•ns<• to moclt·mteh· \ t'"ll'lllar. an· alnrndanr in most l'u:-·t· falb ITa­hlt>:! I and r •. ,._ •. mhlt• "t·arapat'l.-··lik•_. material dt>~t·rilwd I rom \'okanir dorm.•s and nhsidian lan1 fl1•w~ t Fink amll\·lanh',\-. IW-i';; H£•il-:t•n and \\'.,h]C'tz, I~IH";'J. Similar clasts art• also ahun­

lhllrt in ignimbritE·:-; produn•d h,\· t hest• nupt ions. The ,-.,ar,;t·-gr:tim·d I'll\'!• Format ion pumic('­

tlow:;. dt·n~t· hiock-and-Hsh p~·rociast ic tlnw:;, and relatiwh- thin. lithit·-rich and wt'll strati· lit•d ignimhrilt·:-; I Fig. I-ll fttrt ht•r suggt•st that

\'Ulcaninn <111<1 ,..uhplinian Prupt ions Wt'rt' prt>­

rursory to and m-eompilllied till' gr~1wth and pos;;ihh· !'pisodi<" collapst> of port ion,.. of Tschi­

coma la\'a donws or oversteept•npn lava flows 1c.f., Host• l't al.. lH7fi: Nairn und Self, 1978; Wright e:-t nl., I !lH-la 1. However, ~1'\·t·ral of the upper tt'phra group depo:-.its may havt.> heen

produn•d hy mort• vioh.•nt l,\· explo:<ive erup· \ ionf:, approaching t ht• dispNsal char:t.-tt~rist ic~; of plinian m·ti\it_\· i Walkt·r. IHRII. and tlw up­pi~r g-roup rhyolitt· pumin· foil:-. (C!l and <i~~ 1

art.· alrnnst Ct'Ttainly of plinian t,\'Jlt'. The pres· ~-'ll<'e <•f rnult iplt> fallun its oh·veu t h irk rwss and

the pUll!' it,\' of JhJorJ~· \'l"Sicuiar juwnilt' dast Sin tlwse thickt-r rhyolitic fallllt•positsattt•>-ol to this

probability. \'nlortunatf·ly the limitt•d t>xpo­

sure of till'"(' unit:< nnd tlw highly lllls_\·stPmntic variations in t hirkn('~S of most Puy(' l!·phrn de­po,;it s do not Jll·rmit a pn•n,..t· t-'st imatt• of t>itlwr rlw di~pt'Tsai an·a 11>1 or lrngntt•nt:nion indt•x l F I of \\'alkt-r 1 I Hl:ll.

Tlw earl it•,..t t'X plo~l\'t• ;H·t j,·it y n·pn·,.:pnt I'd in r !w Puvt• fan i,. ,..h, •wn hy sl·\·t·THit·oar-a•-grailwd rh,·od:wilt· Jllllllll'l' !ails anrl 1 hm pumit•t•ous

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mud flow d<·posits. Tlw,.,t· dt•bris-ladt•n mud· flows apparently d;~mmed tht· axial drain:lg(' at the fan toe, forming a wid(':'pread lake i Fig. :l) int•> which ahundant tephra accumulated (Fig. -:a J. Stacked pumirt>ow- mudflows form a promirwnt z.;-, m thick apron around tlw pe· rimeter oft h1· Puyt' fan at this horiwn (Fig. fi)

and an• cor:dat i\'(' trpfan \\ ith thick ~equ<•Hces of intt•riJ!'ddi'CI purna'l'<llls ~ht•t•t flood and bra;ded ~tream ctmglt~tnerates. Sevl!ral exulo­si,·e eruption~ an' recorded in t lw lower .t:J .. fJO m of the fan. each H'qllt'nct• c·tmsist ing of two or m·m~ pumict· falls, thin ignimbrites. and high!:-· pumiceou:; rnudflow ch·posits that represt•nt laterally remobilized portions of primary te­phra units. These seqtwnces are separated hy

. st•vrrdl meter:: of sancis. !!f8\'els, and r·onglom­erates dt>po,;ited hy channelized :;treams, sheet­floods, and mass flows (Fig.;; J.

Explosiw eruptions continued as the fan prograded t~astward into the Espaf10la hasin and wert' aecompanied by in,·reast's in thl' propor· lion!< of CtHtr;,t• dl'hrii' flows and coars~· pumict."­flows. many of whirh WE>r<• rapidly :~t·worked upon emplacement. This period culminated with eruption and emplacement of t:,e lithic­rich Puye ignimbrite and accompanying pum­ice and a1;h deposits. Following this e\'ent. coarst> debris flows charactNized much of Puye fan de­position, as abundant material was being sup­plied from proximal dnme breccias. Fluvial ac­ti\'ity was apparPntly accf'lerated, probably dul.' to cycles of i nnea:<ingl~· t.f!icient incision across the growing fan l>tr~face, and lacustrine systems again began to predominate along tht> fan toe as drainage pattern~ wt>re disrupted by episodic sedimt>nt accumulations. Tht." well preserved nature of most dt'posits in the Puye fan ( espe· cially mudllow~) and the lark of evidence fur abundant vegetation in this semi-arid region I Kelley. 19-:'9: ~fanley, 1979: Dethierand Dem­sey, H~R4) :;uggt'st that dimatic 11uctuations were not significant during this period. hencf:' most sl:'dimentary proc(•;;,-e~ in the fan are rnon· feasibly att rihuterl to chan1ws in \'okanological aud t£'ctcmic TE'!!illl£'"· Cnnt inued siliril' t'TIIJI·

1 • • : 0 ~ , I ,;

11!111~ fnllll tlw Tsrhiro11na/El Ht·dJI.It•I<Js n·n· ters,and ~iJ!IUltaJll'OIIS hasaltir Hl'tivit~• from tlw Ct>rros del Hio volcanic centf!f, re~ulr.ed in the coeval suhaqu<•ous emplacPmf'nt of uhundant fi·h:ic and hHsalt ir t<·phra.

,. :;

The proximal hlol'k·and·a~h llow sPqu;•nct:s uttest I•\ at !Past two t•pi!-.odt·s ol vuk.mian ac­ti,·ity. prt:hahl:-· a~socialt•d with tiH· gravita-1 IOIIHlt·t,llap,.,· nf llll~tab! .. port ioni' .,f 11 litho­log;cally dis! inct i\'<' hornh!t>ncl!•·rhyod:wil(- luva dom<> that has not yt•t het·n id<•ntifit•d in the Ts<"hicomH v"kanic C<·nt<·r. Tht·s<· (•pisorles are also rt'llt·ctt·d distally in tlw fan It~· t:oarse­grained. rwar monolit hologir starkt•d debris flow ~t>quences 1 hat dominate t ht• upper parts of tht• l'uye Format ion (Figs. ~~. 7C: \\'areshack and Turbe\·ilk. in press 1.

Volcanogenic alluvial sequf'n<'f's like the Puye Format inn pre:'en;(• exrellt•nt record~ from vol· canic terrains. An e!'timat<'d lfi .. Jti km:' of largely Tsrhic'(•ma·rlt'ri\'ed vokanicla!'t ic ma­terial etun•ntly rt•sides in the Puyl' fan and an undetermin<·ci. hut undoucibterlly significant . amount of st•diment exists in thE: subsurface be­neath tht' eaf.tern edge oft he Tschi<'oma massif (Fig. 1: Griggs. 1 ~().t ). The large variety of rock 1:V1Jes found as Puye epirlasts (Table 2). com­pared to tht> much more re:;tricted suite ob­H'rved a!' Puye airfall lit hies I e.g .. Figs. 8, II ) or :1mung Tschi<"oma la\'a flows. str"ngly im­plies the former existen<·e of a lit holo~rically hi~hly \'ariabl<· nort ht•asll•rn Tschicoma dome complex that was mpidly denuded fnlluwing ct·s~ation of ,·olcanism. TopographiC' con­straint!' ,:;uggt·st t hut much oft he mat I:' rial shed from this C\Jmplt•x was transported hy east­ward-tl.,wing drainagt• en rnu1<• 111 t hf' ann•st raJ Hio Grant:!<>. Howt·,·er. tlw fairly high rates of aggradation f'\'ident from t lw Puyt> fan. due to tht' sporaciic anrilahility of waiN in this semi­arid rt·gion and ~radual down· fault in~ in the as· sol'iated dt•porenter i Esp.niola basil! of the c-~ntrai Hio (;rande·rift I. gn•atly Pnhanced tlw irworporat ion nf llltrl'h oft Ills ltl:lt«•fl<ll into t lw I 'u:.·e F. •rmat i• •n.

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d· \'IJ

at• nd t <'I Ts

t io tat pll' dist fle< ndj. ('(Ill

salt ste;. cia,., wht· inllt gins I'll('(•

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"l•t·..r l•·at 1.

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at·· .ta· ho­lva the are r ·st·· low tht­and

uye vo I· ' of ma­i an

lint •. . be· 1!'-Sif rock

om· ob· 11 )

im· :ally tome wing

con· shed east· ·stral es of Ul' to

•em i­Ii' as· t' the d the 0 tht>

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( 'ondusions

From this ~tud~ oJ pyroclastic :111its in tht· l'uye Formation, oorth·c-€'ntral New Mexico, we (';t n makl' t ht• f<~ll•m·ing ''lltldll:\ion,; C'Oil('l'rtl ing t lw Late l'lto\'l'lll' ·Early l'lt·i,..tot'l'llt' evolution oft he . .Jeml.'z Mnuntain, ,·okanic lit•ld.

t II The l'uyP .tiluvial system l'•mtains > 1.", km' of \okanll'bstir matPrial dt·ri\'t•d alrno,,t l'Xcl~tsin·ly trow tlw nor!lwastt~nl p:trt of tlw TsdlH'orna \'okanic n•ntt·.- and n·cord,.; t•xp(q. si \'l' vokani:-m a nrlt·pida"t ic sedi nwnt at ion di · n•l'lly n•latt·d 1 o t ht• growl h of Ia rgt· lava clonws. Tht>st• dar it ic :1n:l rhyodacit ic dnmt•s supplit·ci abundant m:ilerwi' to tla· fan in tlw form of l'O<HSI' t•pidasl s dt•riwd from proximal talus slopt!s and pvrod:tst ir matl'rial emphH·t•d as pumin~ fall!' ;~n .i pyroda-:tir flows. At.i<'ast J;}

small-maj!nit ude ( 0.1- 1.0 km' I explosi\'e l'rL:Jl·

t i<ms from t h<> twrt lwaslt~rn T::.chicorna la\'a d•1mes ·are r•~C'orded. as well a!' two t•pisod<'s of ,-ukanian blnrk-and·a~h tlol\\', pnssibly as!'ori­att'd with ~ra\'iiHtionalla\'a domE' lOIIapse. In add it ion, tht· fan contains rhyolit i<' and basalt ir tephra deri..-ed from :-:oun•t•s out side of t ht• Tschicoma cent H.

12 I The> rpcognition of cyl'li('al Puyt• deposi· tiona) sequence.- greatly simplifies an interpre­tation of eruptive ewnts from this dome com­plex. The Puye Format :on represents a distinctive depo!=.itional ml.'gaseqtwnce that re­lleC'ts contemporan~>ous \'okanism from two adjacl•nt volcanic <'<'lll('r:-. t lw Tst·hicoma domt­complex to tlw west and tlw { 't•rros dl•l Hio ba­:-;altic field tn the !'-ou:h. ThP Tschicorna center steadily supplil.'d largl' quantities of volcani· clast ir mate• rial to the pro~raciin~ fan system. whereas \'Okani!'m in the Cerros field stromdy influem·pd sedimPiltation from tl:e basin mar· l,!ins. Preservntion relll'cts the comhinf:'d intlu­t'nt'Ps of a continuous \·olcanidastic sNiinwnt supply in a st-mi -a rio rt'gic·n and post --t Ma tl'<'· tonic acti\·ity ldown·faultingl in the Espaiwla basin nftht> n•ntral Hin (irande rift. In this rl'· spect. the fan is al~•· an intf:'~ral :-tratigraphit· ft·aturt~ of this m:t_ior intracontirwntal cll'prt'"·

~i••n anti 1:- ,•;;sc·ntiallv t'•llllt·mporaJH·~>U' with 11t ht·r allu\·inl s~·stt·ms t·xpostd along 1111' rift.

t :11 \'olnllloj!;t·nic alluvial fucit•s HS c'dlll·

pleH·Iy prest>rved as the l'uye Formation an~ tmo·nmmon in t ht· st ratign•phir rc·c·~trd. sugg~·~t · in~ I hat ::-ul'lt :-c·qm•nt't•s gt•rH'rally h:l\·t· \'t ry low llfl·st·rvatinn pott•ntiHl ar11l that tltt' 1'11:-c· allu· vial !an '" 1 h•·reforp sorrwwhal uma~u::l. Hela 1 i· •II -hip~ lu·t wt·t'll \'okanil'last it· !'I'IJtii•Jif'~'>• and 1 hc-11· sotJrt't.•::-. howcn·r, <lri.' rarely as 1 ll·ar-cul as that oft lw 'I sdlit·om:t-i'll~·t· s:.-stt•n• Sm1ilar "hl\lt·nces an· pn·sl'f\'t•d in mnre I'Olllplicated \·ukanic tl'rrains 1 Hay. l!):,fi: C'hrist i11nsl'n and Bl:tnk. 1!17:!: Fritz :111d Harrison, J!JH."•; Smith. l!l."i7: Smith c•t ul., I!IH71 wlll'rt' SI'VNal voka­nogt•nit· aprons O\'t•rlap and roalest·e. t'orminJ,: widc·spn•nd \'okanidasi ic ""4Ut'rH't•s ··, 10110 m thick. In many olcit~r volcani<: terrains only tlw cli,..wl to micl-port ions of .,m·e ext ensi\'f:' voka­nirla!'tic· fat'it's an·likl'l~·to ht• prt•serwd. henn• t ht· sourn•s oft h<'st' sl'qUPtH'es are ra rc>ly appar­l'nt. J>istal volcaniC' facies may tht•rt•torl' pro­,·ich· 1 ht• tllll~· d lll'S for t lw in t erprt.>l Ht i• mof pn r­t.•rrt t<>rrains, and it will hf:' necessary t.o extract a!- much information a~ pos:-;ihlto from iM>IatE'd \'nk<miclast ic deposits so t ha: t luo rp(·o~tnit ion ,,f di;,;tinct iw Nupt ion s(•qtt(•nn·~ (on any :-.caiE') can fully complt•ment pt:tr••loJ(ie e"aluations.

A(• know lt>dgemen ts

\\'e gratefully acknowled!!P tlw !'\t•w Mt·xico Bllft'au of !\1itwi' and Mim·ral RE'~ources. Si~tma Xi. and Arnl·rican Wt•stern Cnivt•rsities. Inc., in l'onpt•rat ion with collt!HJ..'llt'~ in t ht• Earth and ~pare Sciem·t•s Di\'i~ion nf Los Alamo~ !\a­t innal Laboratorit•!;, for techniral and linanrial ~up port. \\'e thank Phil Kyle. l':t•w :\1l•xico T(·ch, for 1!\AA data. WE• an• also indehtl'd to c;,.,,rJ!t> \\'nlkt•r. Colin \\'il!-'on. Richard Fi~her, Fra;:;er Goff.< ;rant Ht•ikl·n. Da"id \'animan, and lla\·id Broxton fi1r prn"iding u,;l'ful in~ights into till',.(' t·ompliratt•d \'!>kanit· sl:qU<'Ill'\'S. Early n·r,.ions "f this mannst·ript J!re:ttl:-· hc•rwlitPd

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:\l:hdt· .. l ('. ~~·-·• 'i'h•·l't·rrt, ... dl'f H~t•\nkotui,· fit·!cl ~- ~1 :~.-111 :-',, .. :'ntt. :\lit1lo F:t 1d c·.,r~f (~::ide·h .. S.tnT.I Ft• I ···unlr •. pp ~·.1:: !.:.:.

fl.,;,\. H ,\. :-:n:lh. I\. I .ll>•i fl ..... I·:-;. 1~1.;:• :-1r.11: '":r.1pi1h lh.Ji.t'll.' i,ttl.tt• • i \o•h.t:lh (tJ\ k ... IU Ilk ·'•·Uu-/

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H •• Jolrodl!<'. \\' :-; .md \'anun . .n. I l I .. t~'"';· Sp.t!lal and h•m p· ·:'.tl p.tt tt·r!i' nt :\t•c •Lt'!k \ ·~k~illt~rn 111 tlw 11••rtlu•a:o-l ··rn.IHw·.: '.,!. ~u:it lit·ld. :"t•\\ \ft.xan1, F« )~ ("J'ran~. :\rn l;~·up!J,· .... t ·til·•ll 1 .• r:· J .. l:,3.

ll;l!o!rid!=t'. 11·..;. \'anmun.ll.T il!ld Sh·tf!qullah. \1.. 1!11-·:. l.o:h· ~111 ,, l•tJt• lt• Pli••CI'lW dt·H·i· rpl1h'Ut nf t ht• :\ •• n ht rt:

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(",,n·\·. :-= \. ;,nd :"p.lrk:--. H ~ .. 1 .. I~·~'' (~WIIlti1atl\"t• 11tndc·l~ ··I t!u· :.til ·•l.~ .uhl tiJ. ... J,;•r .... ll t\f t•·phr.l fru1n \'nk.:aliJt"

t•r~:p1J•ll1 , .•• !t:n:n!i-. H~lll \",,J. an·•l.. -1,..:: Jt)H J:.!;-,_ t 'hn•tlall••'ll. IU. ;ond BJ.,nk. H.fL .Ir .. ]!1::!. \'nkan••

•lr;Jt 1,:r,.ph• ·•I th•· (lu.Jh'rtl<ln· Hll\olil<· Plait'"' I in Y..t l·•·., ... t.)Jlt· :".tt">ith\i P.trk 1':..:. <~•···I :--=•ir\'., Prnf. l'ap. :.;~tH Hl 1\:•

lh•lhln.ll l' a:;r! lt,·m~•·\·. K ,\. l~"L Ero•~ion.1l hi'l"r~· and '"'' dt•Hlopnwrll on t~u;ttf'rn<tn· ~urfat·e~. north Wt'~l r:.pail··ia Ha<ill. :"'t•\\ \It Xll'll. :"'}•l (it" II. s.l( .... t:.lh :\nnu. Frt·lrll'nnL I itndd• .. pp. :::.!7 :_!:i:'o.

F111k .. JH anri :'\litnl,·\·. C.H. (!1~7 OriJ:in uf pumin .. u,; and)!!"''' tO!Urt'1o in rh\'nlitf' flow' and domf'l'. Ct·ol. Suc .. ~n1 .. :'1w'· Pap.~J-.!·77-~.

Ft,ht>r. P. \' .. HE>ikE>n. I i.H . 1\Jrtnnan. \\'.D.ancl Wt.oh!,•t1. K H .. 1!ll<4. l'rrrro~ dd H .... ;-;,.w ~'l"xiw. maar!<. •:os tTran• .-\m.\ieoph\·, l·niunl.t;f,: ((4:>.

Fri~t. \\' .1 ... t:~o! ll.lrr: ... ,n. S. l'•".'· Earl~ Tt•rli.trvvnl, .llli d:!,lic dq•·••l:' ,,, 1lw :"'••rtlu·tn !(,,.·k~· \luuntarn~. ln. H.\1 Floc~· J:ld S.~. K<tpkm • Editnr~ r. C<:nuzuir l'a· ll'uj!t'••)!raph' ,,f \\·,.;r.,· .. ntral l.'.S. Hurky \luunl;illl :-;,., t~o•n·:'El'~L 1 >~:n,..-r. 1 ·o. PP :1,;:1 -Ill:!.

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\\'ri;.!ht .• J.\' .. HoHlh"l. :'-.1..1.. !"mith. A.l. .. :'p:~rk,;,, B.S..J .. l!razirr. S.A .. H•tst•. \\'.1.. .Jr .. and Stl,"'lrrl~~~~n. H . l!IIHa. Late (~uatrrnary f':t.Jllo•,..,\'1' >ilir'll' \'11kanil'nt "n ~t. l.u­, .• ,~. West lndit•"- (if'IIL Ma~ .. 1:?L 1 ·I ft.

Wridll •• 1.\' .. Turht•\'illt·. B. I' ami SelLs .. l~tt<4h. l'linian pumit't' dt•t>tt>it,.. ut' t ht· .Jt•mt•l :\l,tlmtam,.. !'\•·w :1-l••xi<'"· EO~ ('!'ran~. :\m. l:t•ttph\·~. l'nion l. r.r,: 11:'4

I I

Journal of volcanology and geothermal research

-------··-··

Editor-in-Chief

A .R. Me Birney Center for Volca'lology, Unovcrsoty of Oregon. Eugene. ()A 9 7403. US A

Editorial Board

P.E. Baker, Nottongham

A. Bauza, Evanston. IL

G. Bodvarsson. Corvalhs. OR

Y. Bothnga. Parts C.K Brooks, Copenhagen

H. Craog. La Jolla. CA R.R. Dibble. Wellington

D. Dzurtsin, Vancouver. WA

A.J. Ellis, Welhngton

R.V. Fisher. Santa Barbara. CA

J.G. Fotton, Edonburgh

M.O. Garcoa. Honolulu, HI

P. Gasparino. Naples

T.M Gerlach. Albuquerque, NM

Scope of the journal

A Grunder. Corvalhs. OR

M L Hall. Guoto B F Houghton. Rotorua

C P Jaupart. Pans

AM. Jessop. Cet~arv. Alta

A 0. Johnston,lugenc, OR

J Klcrkx, Tervuren I Kusnoro, Tokyo

F Le Guern. Gof·sur·Yvette

J.F Luhr. St. Lours. MO

S 0 Malone. Seattle. WA

B 0. Marsh. Battomore, MD

E A K. Moddtemost. Sydney. N.S.W

K N.:rkamura. Tokyn

H Poehler. Ti.Jbonyen

G R Robson. Thorsk

W I Rose Jr .. Houuhton. Ml

L. Aybach, Zunch R Scandone. Naples S Self, Arlington, TX

D A Sw'lnson, Vancouver. WA

R.l Tilhng, Mento Park, CA

E. T ryggvason. Reylqavok

P.M. Vincent, Clermont-Ferrand

S.D. Weaver, Chrostchurch

C.J.N Wilson. Cambrodge

Papers coverong the folio wong aspects of volcanology and geothermal research woU qualify for publication on the Joumal of

Volcanology and Geothermal Research: Ill geochemocal aspects - gcochemostry of votcanoc rocks, geoc.hemostry of votr.anoc

gases and related products. osotope studoes; (2) petrOIC>gocal aspects -magma genesis and magma evolutton. p!llrolo.;Jv of

volcanoc rocks; (3) economo.: aspects- ore deposots related to volcanic rocks, geothermal energy; (4) geotlhysocal aspects­

physic:al properties of volcanoc rocks and magmas. heat flow studoes. physocal volcanology, volcanoc seosmology, "olcanoc

surveillance. geophysical exptoratoon for geothermal resources; (5) tectontc aspects - relatton of volcan~sm to global and

regional tectonoc processes. 16} envoronmental aspects- volcanic gases and theor effect on the atmosphere.

Types of contributoon to be published are. (1) research papers. (2) revoews. (31 short communocauons, (4)letters. (5} book

revoews and (6) announcements

Publication schedule and subscription information

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Publocaroon of aosrracrs an<1 conrnn:~ Currt'~ ·. ~ Ab~.tr;.oct~ or contents of !Ius 1ourna' a11· pul••·;,•wo "' ~ ,; I ·, 81/JihJ.olri)flhy ;mol lud•·• of C;t•<l•ogy Cherrh< .rl Allslr.KI5. ,

Cor·rP.nrs. Geo Abslfacrs and Monetillogr~dl At•strac :~

a/ of a me IV of

:ts-:a me and

)()()k

1988

y has

. The

nuna. 5outh edl at •S are

orr11a· (212)

r'

JOURNAL OF VOI.CANOLOGY AND GEOTHERMAL RESEARCH

VOLUME 36 (1989)

·~

r

r

Journal of volcanology and geothermal research An international journal on the geophysical, geochemical, petrological, and cconoml(: aspects of geothermal and vCllc3nological research

----------- --·-------- -·--·~ - ·-- ·····- -------··- .. ···- -·-·-··.

A R McBor,ey. Euge•1C. OR

P.E. Baker. Nottongham R Batoza. Evanston, ll G. Bodvarsson. Corvalhs. CR Y. Bottonga. Pans C.K. Brooks. Copenhagen H. Craig, La Jolla. CA R.R. Dibble. Wellongton 0. Dzurisin. Vancouver. Wl~ A.J. Ellos. Wellington R.V. Fosher. Santa Barbara. CA J.G. Fitton. Edinburgh M.O. Garcia. Honolulu, H! P. Gasparini. Naples T.M. Gerlach. Albuquerqut!, NM A. Grunder. Corvallis. OR ML Hall. QUitO B.F. Houghton. Rotorua C P . .:aupart. Paris A.M. Jessop, Calgary, Alta A D. Joh.'lston. Eugene. OR

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J Klerkx, Tcrvumn I. Kushoro, Tokyo F. LP. Guern. Gof-sur· Yvelle J F. Luhr. St Louos. MO S.D Malone, Seattle. WA B D. Marsh. Ba1t1more. MD E A.K. Middlemost. Sydney. N.S.W K Nakamura, Tokyo H. Poehler, T ubingen G.R. Robson. Thirsk WI Rose Jr., Houghton. Ml L. Rybach. Zunch R Scandone. Naples S Self, Arhngton. TX D A Swanson. Vancouver. VIlA R I Tllhng. Menlo Park. CA E. Tryggvason. Reykjavik PM. Vmcent. Clermont-Ferrand S D. Weaver. Chnstchurch C J N. W1lson. Cambndge

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VOL 36 (1 989)

ELSEVIER. AMSTERDAM- OXFORD- NEW YORK- TOKYO

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PITON DE LA FOllRNAISE VOLCANO, HEUNION ISLAI"D

A K \ld11H7"EY tEditor•

Contrn!,;

l1atrodw.:ti•,1~

·1 ltt· ,,ft sh•,rt.· n1111 illUat l•'nnl an ;tt ll\ •· h:t.-.;th J,· '"''"··•h•• l•t1tlll ,ft _I;: F••Hrt1.11,,. t ltt~lllll•Hl 1..-l.uu\. 1ruhnn '),·•··.tn t .

. true I ural and ~·.-.un•.•r}JhoJtJ::i, alt,ah·rprt•Lat t•Hl fr••nl St·:• Ht·.uu lllaPJJin&:

.f. F. , .. :nut ami r \'inn•J:I I ( '!•·rlll•tllt F•·rr:o•Hl. Fr:•nn·l. at . .! I' 1\u .. hrlt·r.· tl.rt H,;tminn. Fraun•l ......

I 'ompl<•tl' ~ravity study oi l'llun •ll·la Fournai~t' \'~tlnwu. l<•·•m1"n (,iand

IJ. Huu~~•·t and A.l.t·~qu .. r 11\l .. :llpf'lli•·r. Fr:m•·•·l. /1. Bunm.,·tll•. ancl.I.·F l.t'nat tl"h·rrrllmt F<·rr;tncl. Fran•···· :r;

l·:rupl ivt• h istury c•f tlw l'it<~n rl•· ht F•turna i~t· vukan11. H,•uniun J,l,mtl. ln<lutn I )n·an

I' .. \'. ( ;;11.,1 i r;if·!'o\lf · Yvt•l It·. Fr~llt't' I anrl I'. !':it I i\'t•l I Ors<1~·. Fr.llln·) ..... ... ............. ................... . . . ..... .... .. . i'o:l

.·\ ~wtistical and pro•lmhili>;ll•· ~tudy .,f thl" hi~l11ri•· ac·ti\'lt\' ul l'tl~>l. <it• Ia J..,,,rn,1ts.·. H•:uniun (,land. lnd11111 On•;,n

l.. ~tieltje> and P. MnuttJu il..a Ht:uni•lll. Fnuwr-1 ............................ ........... .................................. ...... ..... ........ ,;·;

Tbt• Decl'ml}('r 4. l!lR:I tu Fehn111ry 1?<. l!184l'ruptiun of l'it .. n d•·la Fourn:•i~t· C J.<t Hruni""· lndif!ll0n·anl:

d••..criptio>n and in•t'I'J)ff'l<tl;un

.f..F. I.Ainat (CII.'rmunt·F~rrand. Frunn·l. I'~ Ha,·ht-IHy ( Lt Hhuinn. Frau.-c 1. A. Hnnnt·v:ll,• ;,nd 1'. Tmll,..

1\.'INinnnt·Ft·rranc!. Frant:t't .. f..J..!.'ht'lllint~and H. lh•lunt~t· ·l';•ri~. Fram·t•l.................... ........ .... ......... .... .. .. )>~

The (~rand Brule explurntiun drilling: llt'W clata ontlw J., .. p fralll<'""'" ttf tht· Piton d•· Ia Fnurm• ,,.,.. ,·.,lnmn. l':trl I

Litho!'lralij!raphi<' unit.> and vul<'lln•J~Irw:turalnnplirati•m'

.J.P.'Han~·~tn. P.l..ert'bc•ur and T. Aug~ IOrll'an~. Fr<~nrl' • ................................. ......... : ...... ......................................... I 1:1

The <;rand Brltle exploratiun drillinj!: new d..1t.1 nnthl'Ot't'IJ framrw•ork uf th~> l'tlnn dt•la F•lllrll>ti~•· ,·.,kann. l'arl ~

St•C'nndury mirlf'ral!'

1'. Lerei><••H .. J.P. Haru;nn and T. AugP (Orlean~. Frunn•i............. ....... .... .............................. .. 1:.!!•

The Grand Brule t'xplnration drilliug: n~w data nntht- del'Jl l'rumewnrk ut :h<· i'itnn dt•l:r Fuun111i~r \·ukanu !'art:~

Mineral chemistry of the t·umulatt' rocks

T. A•1ge. P. Lerehour and .J.P. Hant;nn (Orl,•an~. Fran<'t') ............................................................................................ 1:1~

G•~•thermal mndt'l of the Sala1.ie Cirque I H~unionl!'.land ): vnkarm: 1111d ~tnrctural implit'llliun1'

,J. Deman~e. P. Chovelon and P. l'uvilland cOrltoans, Franl·r) ........................................................................................ If,: I

The Salazie Cirqut' ignimbriw ( l'itun des Nr.i~l's vokano. JU:umon Island): l'hrunustratil(raphv. d~~rritll;•m and

significanre of lithic fragllll'llli' and eruptivr mt'Chanisms

P. Rocher 1 Paris. France l and D. \\-'eswrcamp (Orleans. Fratwd ............................... ................... .. ......................... I;;

R.euninn hot.~pot activity through Tertiary time: Initial resuhs from tht Ot·ean I>nllinl! Prul(ram. l..t•J: I H1

H.A. Duncan .• J. Bal"kman and L. l'etersen ......................................................................................................................... 19:1

!\.larch 1986 eruptive l'pisndes 111 Pi tun d~ Ia Fuurnai.;t- \'ulcano ( H~union Isla nell

H. Dl'lorm(' (Pari~ and Plain~ Ul's Cafrt-s. !.a Ht•uniun, Frant·l' 1, P. Ba<·hi-l!·f)· (J .a Ht:uniun, Frann·). I'.A Hl•un

and ,J.L. C'ht'min~ I Paris. France l. J.r'. !lela rut• and ,J.C. l>t:lmund (La Wuninn. t'ranc·rl. A. Hirr• and .l.t '.

Lepine (Paris. France). P.M. Vin.:ent (Clermnnt·Ferrand. Frant·r 1 and.J. Zlotni•·ki (!'uri~. Fram·e ) ....................... 19!t

The beginning of the J98.'i -198i erurltivl' t•yde at Piton dP Ia F•mrnaise I I..a Heuninn 1: m•w insi~:ht1; in thl•

ma11matic and vukann·U'•'lllnic systems

.J.·F. l..?natiC'li'Ulllliii·Ferrand. Frnm~e), P. Bal'h~lef)· ll.a !{•'union, Frant·el. A. Bmllll'\'illt· tCII'fm••nt-1-'•.•rrand.

Franc(' l and A. Him I Paris. Franl'e \.. ....................................................................................................................... :.!O~t

I I

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