JOURNALOFPETROLOGY VOLUME46 NUMBER11 PAGES2197–2224 2005 doi:10.1093/petrology/egi052 Wolf Volcano, Gala´pagos Archipelago: Melting and Magmatic Evolution at the Margins of a Mantle Plume D DENNIS J. GEIST1*, TERRY R. NAUMANN2, JARED J. STANDISH3, ow n MARK D. KURZ4, KAREN S. HARPP5, WILLIAM M. WHITE6 loa d e AND DANIEL J. FORNARI3 d fro m 1DEPARTMENTOFGEOLOGICALSCIENCES,UNIVERSITYOFIDAHO-3022,MOSCOW,ID83844,USA h ttp 2DEPARTMENTOFGEOLOGY,UNIVERSITYOFALASKAANCHORAGE,ANCHORAGE,AK99508,USA s://a 3DEPARTMENTOFGEOLOGYANDGEOPHYSICS,MASSACHUSETTSINSTITUTEOFTECHNOLOGY/WOODSHOLE c a d OCEANOGRAPHICINSTITUTIONJOINTPROGRAM,WOODSHOLE,MA02543,USA em 4DEPARTMENTOFMARINECHEMISTRYANDGEOCHEMISTRY,WOODSHOLEOCEANOGRAPHICINSTITUTION, ic.o u WOODSHOLE,MA02543,USA p .c o 5DEPARTMENTOFGEOLOGY,COLGATEUNIVERSITY,HAMILTON,NY13323,USA m /p 6DEPARTMENTOFGEOLOGICALSCIENCES,CORNELLUNIVERSITY,ITHACA,NY14853,USA e tro lo g y RECEIVEDJUNE10,2004;ACCEPTEDAPRIL11,2005 /a ADVANCEACCESSPUBLICATIONJUNE13,2005 rtic le -a b Wolf volcano, an active shield volcano on northern Isabela Island same sources. These melt generation conditions are attributed to s in the Gala´pagos Archipelago, has undergone two major stages of melting in a thermal and mechanical boundary layer of depleted trac caldera collapse, with a phase of partial caldera refilling between. asthenosphere at the margins of the Gala´pagos plume. The lower t/46 Wolf is a typical Gala´pagos shield volcano, with circumferential degrees of melting and extraction from deeper levels result from a /11 vents on the steep upper carapace and radial vents distributed in thickerlithosphericcapatWolfthanexistsattheGSC. /21 9 diffuseriftzonesontheshallower-slopinglowerflanks.Theradial 7 /1 fissures continue into the submarine environment, where they form 4 3 3 moretightlyfocusedriftzones.Wolf’smagmasarestrikinglymono- KEYWORDS:caldera; Gala´pagos; mush; partial melting; plume 59 tonous:estimatederuptivetemperaturesofthemajorityoflavasspan 9 b atotalofonly22(cid:1)C.Thishomogeneityisattributedtobufferingof y g magmas as they ascend through a thick column of olivine gabbroic ue mush that has been deposited from a thin, shallow (<2km deep) INTRODUCTION st o n subcalderasillthatisinathermochemicalsteadystate.Wolf’slavas Wolf volcano forms the northeastern part of Isabela 1 4 havethemostdepletedisotopiccompositionsofanyhistoricallyactive Island in the western Gala´pagos Archipelago (Fig. 1) A p icnotmrappolsaittieonoscea(enxciespltanfdorvo3lHcaen/o4Hone)thinedipsltainngeutisahnadblheafvreomisomtoipdi-c ashnideldisvaolcgaenoomo(Wrpihlloialomgsic&al MarccBheirtnypeye,o1f97a9)G. aItla´ipsagthoes ril 20 1 ocean ridge basalt erupted from the Gala´pagos Spreading Center tallest Gala´pagos volcano (1710m) and has undergone 9 (GSC)250–410kmawayfromthepeakofinfluenceoftheGala´- cyclic filling and collapse of its caldera, providing pagos plume. Wolf’s lavas are enriched in incompatible trace an opportunity to assess the lithospheric evolution of elements and have systematic major element differences relative to Gala´pagos magmas under changing conditions. Despite GSC lavas, however. Wolf’s magmas result from lower extents of thesimilarityofitsvolcanicfeaturesandthelithospheric melting, deeper melt extraction, and a greater influence of garnet evolution of its magmas, Wolf volcano differs from the compared with GSC magmas, but Wolf and the GSC share the other western Gala´pagos shields in that its lavas have (cid:1) The Author 2005. Published by Oxford University Press. All *Correspondingauthor.Telephone:208-885-6491. rightsreserved.ForPermissions,pleasee-mail:journals.permissions@ E-mail:[email protected] oxfordjournals.org JOURNALOFPETROLOGY VOLUME46 NUMBER11 NOVEMBER2005 3°N Darwin I. Wolf I. D Galápagos Spreading Center ow n Pinta loa d Marchena e d RR Genovesa fro m h E WD Santiago 0° ttps://a c A a Santa d Fernandina e m SN Cruz ic CA .o San Cristobal 1°S up Isabela .c Española 2000 m om Floreana /p e 92°W 88°W trolo 3000 m gy /a Fig. 1. Map of the Gala´pagos Islands, showing location of Wolf volcano and the Gala´pagos Spreading Center. Arrow indicates the absolute rticle motionoftheNazcaplate.VolcanoesonIsabelaIslandare:E,Ecuador;W,Wolf;D,Darwin;A,Alcedo;SN,SierraNegra;CA,CerroAzul. -a RR,RocaRedondavolcano. bs tra c unusually depleted Sr, Pb, and Nd isotopic signatures. partofthemantle’sTransitionZone(Hooftetal.,2003). t/4 6 ThispaperdescribesthevolcanichistoryofWolfvolcano The geophysical data thus support geochemical and /1 1 for the first time, assesses the petrological processes geochronological evidence that the western Gala´pagos /2 1 responsible for the evolution of a remarkably homogen- volcanoes are formed by a deeply rooted mantle 9 7 eous suite of basalts, and describes a new model for plume (e.g. Morgan, 1971; White & Hofmann, 1978; /14 3 meltingintheuppermantleadjacenttoamantleplume. Geist et al., 1988; Graham et al., 1993; White et al., 3 5 1993; Sinton et al., 1996; Kurz & Geist, 1999; Harpp & 99 White,2001). by g One of the most notable aspects of volcanoes in the u GEOLOGICAL DEVELOPMENT OF e WOLF VOLCANO tGemalaa´ptiacgospsaitsiathladtistthreibiruitsiootnop(Wichcoitme p&osHitioofnmsahnanv,e1a9s7y8s-) st on 1 Regional setting that has been attributed to dynamic mixing between a 4 A WIslaonlfdi,swonheicohfasilxonsghiewldithvoFlecarnnaonedsitnhaatfomrmakethuepwIseasbteerlna mWahnitteleetpalul.m,1e9a9n3d;Kthuerzu&ppGereimst,an19tl9e9(;GHeiasrtpept a&l.,W1h98it8e;, pril 2 0 subprovince of the Gala´pagos Archipelago (Fig. 1). This 2001). The critical observation is that volcanoes of the 19 region is characterized by volcanoes with a distinctive centralpartofthearchipelagohaveisotopiccompositions morphology, including ‘inverted soup-bowl’ cross-sec- within the range of mid-ocean ridge basalts (MORB) tions and deep calderas, as well as frequent volcanic from this part of the world, whereas the volcanoes to activity, including more than 50 witnessed eruptions the north, south, and west have progressively more (McBirney & Williams, 1969). Recent seismic studies plume-likeisotopicratios.Wolfvolcanohasbeencritical indicate a low-velocity anomaly extending through the to the development of these models, because it has the uppermantleSWofFernandinavolcano(Toomeyetal., mostisotopicallydepletedlavasinthewesternpartofthe 2001), and this anomaly overlies an anomalously thin archipelago(Geistetal.,1988;Whiteetal.,1993). 2198 GEISTetal. EVOLUTIONOFWOLFVOLCANO,GALA´PAGOS Wolf volcano lies on lithosphere that is about 10Myr WoodsHoleOceanographicInstitutionusingtechniques old, as estimated by extrapolating seafloor magnetic reported by Kurz & Geist (1999). Magmatic helium iso- anomalies from outside the archipelago (Wilson & Hey, topiccompositionsweremeasuredbycrushingolivinein 1995). It is immediately west and south of a curved avacuum.Thecrushedolivinewasthenfusedtorelease boundary that is thought to separate lithosphere that is cosmogenic helium for age determinations (Table 4). in Airy compensation to the east and north from litho- Argon age measurements (Table 4) were carried out on spherewithanelasticthicknessofabout12km(Feighner whole-rock samples by Dr Robert Duncan of Oregon & Richards, 1994). Gravity modeling indicates that the State University using techniques described by Sinton crust beneath Wolf volcano is (cid:2)11km thick, although et al. (1996). Holocrystalline samples were selected, and there is a fairly steep gradient in crustal thickness in this groundmasswaspickedforanalysis.Sampleswereincre- area (Feighner & Richards, 1994). Wolf is bordered by mentallyheatedinfive150(cid:1)stepsformeasurementofthe D young volcanoes to the north (Roca Redonda), west argonisotopes.Agesarecalculatedbothonisochronand ow n (Ecuador), and south (Darwin), but a >3000m deep age-spectrum(‘plateau’)diagrams. lo a trough lies immediately east of it. Because the absolute Strontium, lead, and neodymium isotopic analyses d e mthoistioinndoicfattheesNaaznceaarPlaatbeseisn9c1e(cid:1)o(Gf rvioplpca&niGsmordfoorn,o1v9e9r0)a, wOecreeanpoegrfroarpmheicdIantstCituotrinoenll(UTanbivleer3si)t.ySaanmdpWlesowodesreHleoale- d from million years in this part of the archipelago before Wolf chedinwarmHClbeforedissolutiontoremovesaltspray h ttp emerged. and weathering products. The analyses at Woods Hole s were by thermal ionization mass spectrometry (TIMS), ://a c andanalyticalprocedureshavebeenreportedbyKurz& ad Methods Geist(1999).AnalyticalproceduresatCornellhavebeen em ic The subaerial part of Wolf volcano was mapped and reported by Blichert-Toft & White (2001), and data for .o u samples were collected duringafield campaignin1995, threesamplesreportedinTable3werealsopublishedin p .c using World War II-era aerial photographs as a base. thatwork. Severalof the samples were analyzed inboth o m Multibeam sonar, side scan sonar, and submarine sam- laboratories, and there is reasonable agreement, but the /p e ples (D3 and D4 samples) were collected by dredging variabilityisbeyondmeasurementerrorinseveralcases. tro duringthe2001DRIFT4cruiseoftheR.V. RogerRevelle Thedifferencesbetweentheanalysesaresmallcompared log y oftheScrippsInstitutionofOceanography(Fornarietal., with the isotopic variation in the region and even Wolf /a 2001; Kurz et al., 2001; Harpp et al., 2002). The MR-1 volcano itself. Where duplicate measurements are avail- rtic le side-scan sonar system, which is a 11/12 kHz towed able, the average values are used for plotting and -a b system,wasusedtoimagetheseafloor.Thesystemesoni- geochemicalmodeling. s fiestheseafloorandcollectscoregisteredbackscatterand trac phasebathymetric data (Rongstadt, 1992; Davis et al. t/4 6 1993).Theside-scandataaregriddedat8mspacing. Geology of Wolf volcano /1 1 Majorandtraceelementanalysesweredeterminedby ThemostdistinctivefeaturesofWolfvolcano,aswithall /2 1 9 X-ray fluorescence (XRF) at Washington State Univer- Gala´pagos-typeshields,areitsshapeandthedistribution 7 /1 sity according to techniques described by Johnson et al. of volcanic vents (Figs 2 and 3). Wolf’s vents occur in 4 3 (1999),whoreportedanalysesofinternationalstandards. threeclusters:(1)lower,radiallydistributedflankfissures; 35 9 Thedataandtheirrelativeprecision,reportedasrelative (2)arcuatefissuresalignedsubparalleltothecalderawall; 9 b standard deviation on a triplicate analysis, are given in (3) caldera floor vents (Figs 2 and 3). The radial fissures y g Table 1.DRIFT4glasseswereanalyzedontheCameca are concentrated in three zones that extend north, NW, ue s Camebax electron microprobe at Washington State andSEofthesummit(Fig.3).Youngsubmarineventsare t o University.Acceleratingvoltage was15kV.Adefocused identified in the bathymetric and side-scan sonar data n 1 4 beam was used, and sodium intensity was monitored as and form ridges that extend seaward from the north A aalthfuonucgthiotnhisowf atsimneotaansdignciofircraenctteedffefcot.rFvoorlamtiolisztastaiomn-, asunbdmNarWinesuebnaveirrioanlmveenntt,ctlhuestevresn(tFsigfosr2mamndor3e).shInartphlye pril 2 0 1 ples,twopointsonthreeseparateshardsweremeasured delineated ridges than on the subaerial part of the vol- 9 and averaged. Mineral compositions were determined cano.Themottledtextureontheside-scansonarimageis with the Cameca SX50 microprobe at the University of a likely indication of pillow lavas and mounds separated HawaiiusingtechniquesdescribedbyGarciaetal.(1995). byfragmentaldebrisandsediment. Rareearthelements(REE)weremeasuredonasubsetof The subaerial clusters of fissures are unlike Hawaiian samples(Table2)atLawrenceUniversitybyinductively and Icelandic rift zones because they are much less coupled plasma mass spectrometry (ICP-MS); analytical focused, hence they are referred to as ‘diffuse rift zones’ detailshavebeenprovidedbyHarppetal.(2003).Helium (Geist et al., 2003), and they impart asymmetry to the isotopic compositions (Table 3) were determined at volcano (Fig. 2). The NW and north diffuse rifts extend 2199 JOURNALOFPETROLOGY VOLUME46 NUMBER11 NOVEMBER2005 Table 1: Major and trace element analyses of Wolf lavas W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 1 2 3 4 5 6 7 8 9 10 11 12 Lat.(0(cid:1)): (cid:3).05 .0028 .02 .03 .0309 .0311 .0266 .021 .0163 .0088 (cid:3).001 (cid:3).002 Long.(91(cid:1)W): .41 .3619 .37 .33 .3230 .3230 .3206 .319 .3166 .3175 .325 .327 Unit: Fuv Ry H(1984) Ry Ry Ry Ry Ry Ry Ry Ry Ry SiO 48.97 49.42 49.18 49.13 49.35 48.51 48.84 49.53 49.26 49.38 49.12 50.02 2 AlO 14.69 14.49 15.65 14.23 14.33 14.42 13.95 14.29 14.33 14.30 14.32 14.67 2 3 D TiO2 3.21 3.22 2.71 3.23 3.21 3.25 3.33 3.31 3.09 3.10 3.09 3.05 ow FeO 11.78 11.76 10.47 11.64 12.07 11.48 12.52 11.76 11.81 11.86 11.74 11.05 nlo a MnO 0.19 0.19 0.17 0.19 0.19 0.20 0.20 0.19 0.19 0.19 0.19 0.18 d e CMagOO 106..7258 161..0107 116..8450 106..8171 160..8166 106..9227 150..4609 160..6095 161..1373 161..1483 116..1288 161..0740 d from K2O 0.56 0.54 0.44 0.57 0.54 0.54 0.56 0.58 0.52 0.52 0.52 0.50 http NaO 3.26 3.42 3.03 3.44 3.28 3.19 3.42 3.45 3.05 3.10 3.10 3.18 s P2O25 0.40 0.38 0.31 0.39 0.39 0.39 0.41 0.41 0.34 0.34 0.34 0.36 ://ac a Total 100.09 100.59 100.22 99.81 100.38 99.16 99.32 100.26 100.09 100.41 99.89 100.75 d e Mg-no. 48.7 48.3 52.1 48.3 47.6 49.3 44.8 47.8 48.9 49.2 48.8 51.9 mic Sc 46 49 46 39 35 31 30 29 33 30 35 33 .ou p V 371 376 310 366 368 370 377 369 372 382 382 358 .c o Ba 91 112 88 94 114 115 116 114 113 116 108 99 m /p Rb 5 5 5 7 7 5 6 6 5 5 6 6 e Sr 376 384 391 380 380 376 353 380 388 392 387 375 trolo g Zr 236 224 189 236 234 232 242 247 207 205 205 220 y /a Y 35 34 29 36 36 35 37 37 31 31 31 33 rtic Nb 19 18 15 19 19 18 19 20 18 17 17 16 le -a Ga 24 21 21 24 23 20 24 24 23 20 22 22 b s Cu 95 88 100 76 73 228 76 80 102 100 105 109 tra c Zn 100 103 87 102 96 104 110 105 97 98 101 94 t/4 6 /1 1 /2 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 1 9 13 14 15 16 17 18 19 20 21 22 23 24 7/1 Lat.(0(cid:1)): (cid:3).0058 (cid:3).0058 (cid:3).0079 (cid:3).0053 (cid:3).0055 (cid:3).0055 (cid:3).0055 .003 .0032 .003 .003 .006 43 3 Long.(91(cid:1)W): .3514 .3514 .3462 .3487 .3395 .3395 .3395 .361 .3612 .361 .361 .359 59 9 Unit: Ry Ry Ry Ry Fy Ry Ry Ry Ry Ry Ry Cf b y g u SATiilOO2O223 41843...062427 41843...490420 41284...984906 41384...234690 41394...630252 41384...292357 41394...531467 41384...052534 41383...369196 41832...759722 41287...321435 41286...999076 est on 14 A FeO 11.88 12.14 11.22 11.64 12.24 11.42 11.87 11.30 12.38 11.06 9.21 10.39 p MnO 0.19 0.20 0.18 0.19 0.20 0.19 0.20 0.19 0.20 0.19 0.14 0.17 ril 2 0 CaO 11.20 10.39 11.29 10.92 10.18 10.90 10.42 11.09 10.60 11.92 12.18 11.38 19 MgO 6.34 5.78 6.51 6.04 5.57 6.04 5.74 6.26 5.97 6.60 6.21 4.90 KO 0.51 0.60 0.54 0.57 0.63 0.57 0.60 0.50 0.54 0.40 0.30 0.49 2 NaO 2.99 3.25 3.62 3.36 3.62 3.28 3.38 3.16 3.24 2.95 2.42 3.18 2 PO 0.34 0.42 0.57 0.48 0.45 0.40 0.43 0.36 0.38 0.29 0.24 0.34 2 5 Total 99.39 99.14 100.19 99.25 99.88 99.24 99.70 98.68 99.27 98.62 98.42 99.68 Mg-no. 48.8 45.9 50.8 48.1 44.8 48.5 46.3 49.7 46.2 51.5 54.6 45.7 2200 GEISTetal. EVOLUTIONOFWOLFVOLCANO,GALA´PAGOS W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 13 14 15 16 17 18 19 20 21 22 23 24 Lat.(0(cid:1)): (cid:3).0058 (cid:3).0058 (cid:3).0079 (cid:3).0053 (cid:3).0055 (cid:3).0055 (cid:3).0055 .003 .0032 .003 .003 .006 Long.(91(cid:1)W): .3514 .3514 .3462 .3487 .3395 .3395 .3395 .361 .3612 .361 .361 .359 Unit: Ry Ry Ry Ry Fy Ry Ry Ry Ry Ry Ry Cf Sc 36 37 40 34 34 33 32 35 36 39 28 30 V 385 395 359 372 390 381 388 352 390 378 272 334 Ba 125 131 127 125 125 122 124 98 118 90 83 108 Rb 5 7 7 5 6 5 6 6 5 4 3 6 D o Sr 391 376 388 389 376 385 376 388 389 317 382 415 w n Zr 207 249 209 241 272 238 258 218 238 180 154 211 lo a d Y 31 37 31 33 41 35 38 32 36 33 23 32 e d Nb 17 20 17 20 20 19 21 17 17 13 11 15 fro Ga 26 22 21 20 23 22 23 24 25 20 19 20 m h Cu 99 122 108 51 107 90 92 74 112 y153 82 89 ttp s Zn 98 106 93 94 108 94 96 93 103 87 70 89 ://a c a d e W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 m ic 25 26 27 28 29 30 31 32 33 34 35 36 .o Lat.(0(cid:1)): .008 .0080 .008 .0086 .0120 .0120 .0057 .0025 .003 .003 .003 .003 up .c Long.(91(cid:1)W): .357 .3573 .357 .3568 .3539 .3539 .3657 .3665 .367 .367 .367 .366 o m Unit: Cf Cf Cf Cr Cf H(1982) Ry Ry Ry Ry Ry Ry /p e tro lo SiO 49.36 48.63 49.21 49.15 49.31 48.75 48.77 48.87 49.00 49.23 48.85 48.31 g 2 y ATilO2O23 126..5528 142..9668 134..3202 134..1364 126..9747 125..7531 134..0225 162..7214 152..8462 134..2215 134..1125 134..1134 /article FeO 9.90 11.81 11.58 11.88 10.33 10.45 12.01 9.65 10.58 11.98 12.08 11.51 -ab s MnO 0.16 0.19 0.19 0.19 0.17 0.17 0.19 0.17 0.18 0.19 0.19 0.19 tra CaO 12.05 11.35 10.88 11.03 11.48 11.84 11.17 11.62 11.84 10.65 10.76 10.77 ct/4 MgO 6.07 6.18 6.11 6.23 5.26 6.26 6.36 5.72 6.56 5.95 6.02 6.00 6/1 K2O 0.38 0.43 0.52 0.50 0.49 0.44 0.52 0.46 0.41 0.56 0.54 0.52 1/2 Na2O 2.91 3.02 3.25 3.22 3.16 3.01 3.07 3.10 2.95 3.35 3.25 3.21 197 PO 0.28 0.31 0.38 0.36 0.35 0.31 0.34 0.34 0.32 0.41 0.39 0.38 /1 2 5 4 Total 100.21 99.56 99.64 100.06 100.26 99.47 99.70 98.88 100.12 99.79 99.36 98.16 33 5 Mg-no. 52.2 48.3 48.5 48.3 47.6 51.6 48.6 51.4 52.5 47.0 47.0 48.2 99 b Sc 36 40 36 37 32 38 37 38 39 34 36 37 y g V 316 361 378 364 316 324 359 319 335 380 361 362 u e Ba 89 112 106 106 96 94 107 99 82 105 108 107 st o Rb 5 5 6 5 5 5 5 5 4 7 4 6 n 1 Sr 390 370 371 379 410 390 386 407 364 373 373 384 4 A ZYr 12783 13902 23316 22324 23124 13808 23018 23012 13924 25328 23376 23353 pril 20 1 Nb 14 15 17 16 16 15 18 16 14 19 18 16 9 Ga 22 22 22 19 24 20 23 21 19 24 23 19 Cu 98 130 121 108 94 102 101 111 113 104 84 79 Zn 78 98 99 99 y128 86 98 92 91 105 100 98 2201 JOURNALOFPETROLOGY VOLUME46 NUMBER11 NOVEMBER2005 Table 1: continued W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 37 38 39 40 41 42 43 44 45 46 47 48 Lat.(0(cid:1)): .003 .003 .0084 .0084 .0097 .0172 .017 .017 .0167 .0167 .016 .0163 Long.(91(cid:1)W): .366 .366 .3607 .3607 .3618 .3642 .364 .364 .3648 .3648 .365 .3656 Unit: Ry Ry Cf Cf Cf dike Ro Ro Ro Ro Ro Ry SiO 48.55 48.96 48.52 46.13 48.89 49.09 48.96 48.86 49.75 48.33 48.63 48.02 2 AlO 14.33 14.56 13.95 13.55 14.31 14.28 13.98 15.57 13.92 14.25 14.32 14.22 2 3 D TiO2 3.23 3.06 3.71 3.18 3.02 3.15 3.35 2.81 3.48 3.10 3.21 3.02 ow FeO 11.85 11.69 13.18 11.39 11.99 11.76 12.11 10.82 12.30 11.32 11.68 11.45 nlo a MnO 0.19 0.18 0.21 0.19 0.19 0.19 0.19 0.17 0.21 0.19 0.18 0.19 d e MCagOO 106..0702 161..3193 59..1766 150..6398 116..4200 150..7411 105..7689 161..1529 59..0346 161..0027 106..0966 161..4282 d from K2O 0.55 0.49 0.64 0.54 0.51 0.66 0.57 0.42 0.81 0.45 0.47 0.44 http NaO 3.40 3.27 3.57 3.04 3.03 3.29 3.16 3.01 3.55 2.88 3.02 3.06 s P2O25 0.39 0.35 0.49 0.38 0.34 0.44 0.40 0.33 0.68 0.36 0.37 0.34 ://ac a Total 99.21 100.09 99.19 94.46 99.89 98.98 99.19 99.71 99.10 97.96 98.90 98.43 d e Mg-no. 47.4 49.4 41.1 47.1 48.8 46.4 46.0 50.2 42.2 48.7 48.1 50.2 mic Sc 35 40 35 36 39 39 40 33 31 34 35 39 .ou p V 373 367 395 376 360 355 374 312 352 339 340 323 .c o Ba 121 82 122 81 84 110 96 95 151 102 104 97 m /p Rb 7 5 7 7 6 6 4 3 10 3 4 5 e Sr 388 387 379 387 388 382 353 356 349 361 370 372 trolo g Zr 235 213 279 231 207 265 238 201 385 223 229 215 y /a Y 36 32 42 35 31 39 37 34 58 36 35 33 rtic Nb 19 17 23 19 17 21 19 15 29 17 16 15 le -a Ga 21 24 24 23 21 25 26 21 27 24 21 21 b s Cu 76 109 95 113 97 104 116 113 93 105 101 86 tra c Zn 100 93 111 100 96 105 102 93 y121 98 94 97 t/4 6 /1 1 /2 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 1 9 49 50 51 52 53 54 55 56 57 58 59 60 7/1 Lat.(0(cid:1)): .016 (cid:3).0416 (cid:3).0420 (cid:3).0420 (cid:3).0633 (cid:3).05 (cid:3).051 (cid:3).051 (cid:3).052 (cid:3).052 (cid:3).06 (cid:3).06 43 3 Long.(91(cid:1)W): .366 .3885 .3885 .3885 .4083 .41 .39 .38 .37 .37 .41 .41 59 9 Unit: Ry Ry Fv Fv Fv Fuv Fuv Fuv Fuv Fv Fv Fuv b y g u SATiilOO2O223 41843...100908 41384...010365 41393...409148 41286...651194 41394...113135 41843...262578 41373...488865 41384...144084 41383...438322 41383...479028 41852...992070 41287...871542 est on 14 A FeO 12.01 12.08 12.10 10.01 11.81 11.86 12.41 11.85 12.17 12.17 10.69 10.69 p MnO 0.19 0.19 0.19 0.16 0.19 0.19 0.20 0.19 0.20 0.19 0.18 0.17 ril 2 0 CaO 10.84 11.04 10.35 11.91 11.02 10.56 10.30 11.02 10.13 10.34 11.38 11.42 19 MgO 6.04 6.19 5.68 6.07 6.18 5.95 5.54 6.27 5.60 5.65 6.42 4.69 KO 0.47 0.51 0.63 0.45 0.49 0.57 0.58 0.49 0.59 0.64 0.47 0.40 2 NaO 3.19 3.03 3.27 2.88 2.93 3.20 3.26 3.09 3.29 3.25 2.97 3.02 2 PO 0.37 0.34 0.42 0.31 0.36 0.40 0.43 0.36 0.42 0.42 0.34 0.28 2 5 Total 98.38 98.62 99.07 99.13 99.57 98.93 97.91 99.29 97.96 98.76 99.53 99.39 Mg-no. 47.3 47.7 45.6 51.9 48.3 47.2 44.3 48.5 45.1 45.3 51.7 43.9 2202 GEISTetal. EVOLUTIONOFWOLFVOLCANO,GALA´PAGOS W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 49 50 51 52 53 54 55 56 57 58 59 60 Lat.(0(cid:1)): .016 (cid:3).0416 (cid:3).0420 (cid:3).0420 (cid:3).0633 (cid:3).05 (cid:3).051 (cid:3).051 (cid:3).052 (cid:3).052 (cid:3).06 (cid:3).06 Long.(91(cid:1)W): .366 .3885 .3885 .3885 .4083 .41 .39 .38 .37 .37 .41 .41 Unit: Ry Ry Fv Fv Fv Fuv Fuv Fuv Fuv Fv Fv Fuv Sc 37 34 36 31 36 33 38 37 36 36 37 30 V 348 359 378 312 362 373 399 363 395 382 332 359 Ba 97 123 123 80 101 113 131 105 121 117 95 85 Rb 3 5 6 6 4 7 5 5 6 4 5 4 D o Sr 355 388 381 396 379 373 377 380 363 378 380 389 w n Zr 228 209 247 187 220 241 254 220 252 245 205 173 loa d Y 37 31 38 28 33 37 39 33 38 37 32 28 e d Nb 17 18 21 14 17 20 20 17 20 19 16 16 fro m Ga 22 24 24 21 26 23 25 24 25 24 20 24 h Cu 114 106 117 115 121 96 126 123 92 112 118 121 ttp s Zn 95 97 105 82 101 99 107 94 104 103 98 93 ://a c a d e W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 m ic 61 62 63 64 65 66 67 68 69 70 71 72 .o u Lat.(0(cid:1)): (cid:3).06 (cid:3).06 (cid:3).08 .12 .12 .12 .12 .1386 .1379 .1315 .0803 .0753 p .c Long.(91(cid:1)W): .41 .41 .41 .42 .42 .42 .42 .3742 .3768 .3523 .2933 .2905 om Unit: Fv Fv Fuv Fuv Fv Fv Fv Fuv Fv Fuv Fv Fuv /p e tro lo SiO 47.77 48.61 48.27 49.12 48.91 48.95 48.68 49.12 48.35 48.82 49.27 48.95 g 2 y ATilO2O23 135..1561 117..6213 134..4276 126..7756 134..4062 128..5336 134..3630 135..1299 136..0110 127..5786 126..5761 127..4758 /article FeO 11.94 7.79 12.77 9.98 12.06 9.15 11.91 11.35 11.17 9.96 9.48 9.39 -ab s MnO 0.18 0.13 0.20 0.16 0.20 0.15 0.20 0.19 0.18 0.16 0.16 0.15 tra CaO 9.75 12.74 10.59 11.59 10.24 11.94 10.45 10.80 11.06 11.79 11.79 12.17 ct/4 MgO 7.28 9.50 5.57 5.60 5.72 4.86 5.83 5.59 5.38 5.19 5.57 5.40 6/1 K2O 0.57 0.25 0.48 0.50 0.60 0.44 0.57 0.49 0.45 0.40 0.42 0.40 1/2 1 NaO 3.16 2.16 3.17 3.22 3.45 3.18 3.50 3.32 3.10 3.01 2.92 2.90 9 2 7 PO 0.37 0.19 0.33 0.34 0.44 0.31 0.41 0.38 0.36 0.30 0.31 0.29 /1 2 5 4 Total 99.69 100.21 99.11 100.03 99.09 99.87 99.48 99.72 99.16 99.97 99.19 99.89 33 5 Mg-no. 52.1 68.5 43.7 50.0 45.8 48.6 46.6 46.8 46.2 48.2 51.2 50.6 99 b Sc 32 34 38 36 32 32 33 34 33 32 38 35 y g V 342 204 434 311 391 294 364 348 338 287 290 289 u e s Ba 173 34 110 81 135 86 117 112 106 103 85 81 t o Rb 8 5 6 5 5 6 6 6 5 4 4 4 n 1 4 Sr 378 359 354 409 379 431 383 392 404 415 380 396 A p ZYr 13933 11188 23054 23123 24501 12876 23460 23246 23148 12991 13806 12778 ril 20 1 Nb 24 9 19 16 21 15 19 19 19 14 14 13 9 Ga 24 19 23 24 24 24 24 24 24 22 25 21 Cu 46 58 144 88 117 85 97 100 99 73 81 84 Zn 112 56 109 85 103 75 101 96 97 81 85 78 2203 JOURNALOFPETROLOGY VOLUME46 NUMBER11 NOVEMBER2005 Table 1: continued W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 W95 73 74 75 76 77 78 79 80 81 82 83 84 Lat.(0(cid:1)): .0753 .0691 .0672 .0608 .0608 .10 .10 .09 .09 .09 .08 .08 Long.(91(cid:1)W): .2905 .2944 .2874 .2913 .2910 .30 .30 .30 .30 .30 .30 .30 Unit: Fv Fuv Fuv Ry Fv Fv Fuv Fuv Fv Fv Fv Fuv SiO 48.93 48.86 49.36 48.86 48.96 48.19 49.35 49.37 49.73 49.50 48.77 48.85 2 AlO 13.71 18.10 18.37 14.46 14.43 17.70 14.23 14.30 14.78 14.01 14.29 15.18 2 3 D TiO 3.74 2.32 2.32 3.21 3.25 2.16 3.45 3.25 3.15 3.73 3.13 2.73 o 2 w FeO 13.47 8.99 8.91 11.63 11.71 8.67 12.33 11.77 11.61 12.77 11.84 10.53 nlo MnO 0.21 0.14 0.14 0.19 0.19 0.14 0.20 0.19 0.19 0.21 0.19 0.17 ad e CMagOO 95..6134 152..4755 152..5901 160..9115 160..7044 172..4045 150..3796 160..7006 160..8251 95..6261 160..9298 170..9901 d from K2O 0.65 0.39 0.37 0.54 0.56 0.37 0.60 0.57 0.54 0.68 0.51 0.48 http NaO 3.51 2.89 2.76 3.22 3.17 2.67 3.44 3.29 3.23 3.62 3.23 2.94 s P2O25 0.48 0.28 0.29 0.39 0.39 0.25 0.43 0.39 0.38 0.49 0.37 0.34 ://ac a Total 99.47 100.17 100.93 99.56 99.44 99.65 100.17 99.89 100.67 99.88 99.59 100.04 d e Mg-no. 40.5 53.3 54.2 48.5 47.9 59.2 45.4 47.9 48.8 42.1 48.6 57.3 mic Sc 36 31 35 34 37 33 32 34 34 33 39 37 .o u p V 419 270 273 363 374 257 402 364 379 420 358 330 .c o Ba 149 78 82 110 115 74 110 108 109 145 93 97 m /p Rb 9 4 3 4 6 5 5 7 7 7 4 5 e Sr 371 420 418 382 388 406 373 381 386 363 383 360 trolo g Zr 276 172 170 231 233 158 254 233 228 283 218 200 y /a Y 43 27 27 37 34 23 39 35 34 44 34 31 rtic Nb 22 13 13 20 19 12 20 19 19 21 17 16 le -a Ga 24 23 21 24 24 21 24 24 25 23 22 24 b s Cu 88 76 78 79 116 81 123 123 115 95 117 88 tra c t/4 6 W95 W95 D3A D4C D4E D4F D4A D4B RSD% /11 /2 85 86 1 9 Lat.(0(cid:1)): .0171 .02 .2667 .1900 .1900 .1900 .1900 .1900 7/1 Long.(91(cid:1)W): .2178 .22 .4333 .4128 .4128 .4128 .4128 .4128 43 3 Unit: Fv Fy Sub Sub Sub Sub Sub Sub 59 9 b y SiO 47.97 48.97 48.06 48.90 48.75 48.59 48.66 48.82 0.4 g 2 u ATilO2O23 133..6477 152..6771 135..0142 143..5166 143..0623 143..5178 143..3194 134..6005 00..32 est on FeO 12.08 10.35 10.73 13.04 12.19 13.17 13.61 13.27 1.9 14 MnO 0.20 0.17 0.17 0.21 0.21 0.24 0.20 0.21 0.3 Ap CaO 10.95 11.54 11.48 9.91 10.66 9.98 9.61 9.80 0.1 ril 2 0 MgO 5.56 6.64 6.33 5.02 5.60 5.06 5.06 5.00 1.8 1 9 KO 0.54 0.43 0.56 0.72 0.67 0.72 0.77 0.74 0.0 2 NaO 3.18 3.00 3.93 3.44 3.58 3.60 3.54 3.52 0.9 2 PO 0.42 0.33 0.31 0.39 0.50 0.51 0.50 0.47 0.6 2 5 Total 98.05 99.81 99.72 99.55 99.54 99.52 99.51 99.49 Mg-no. 45.1 53.4 51.3 45.0 40.2 39.8 40.6 40.7 Sc 30 33 3.1 2204 GEISTetal. EVOLUTIONOFWOLFVOLCANO,GALA´PAGOS W95 W95 D3A D4C D4E D4F D4A D4B RSD% 85 86 Lat.(0(cid:1)): .0171 .02 .2667 .1900 .1900 .1900 .1900 .1900 Long.(91(cid:1)W): .2178 .22 .4333 .4128 .4128 .4128 .4128 .4128 Unit: Fv Fy Sub Sub Sub Sub Sub Sub V 388 302 1.8 Ba 118 78 2.7 Rb 7 4 10.5 D Sr 393 378 0.1 ow Zr 251 194 0.3 nlo a Y 40 31 2.0 d e NGba 1293 1251 45..40 d from Cu 123 100 2.3 http Zn 107 91 2.3 s://a c a SampleswithW95prefixarebyXRF;sampleswithDprefixareelectronmicroprobeanalysesofglasses.Locationswithfour d e significantfiguresweremeasuredbyglobalpositioningsystem,andothersestimatedfromaerialphotographs.Here,flank m lavasarebrokenintotwodivisions,onthebasisoftheextentofvegetation:H,historical;Fuv,unvegetatedflanklava;Fv, ic vegetatedflanklava;Ry,youngflowfromcircumferentialfissure;Cf,caldera-fillingfacieslava;Ro,rimfacieslavaolderthan .ou caldera fill. p.c o m /p e tro lo Table 2: Rare earth element concentrations of Wolf lavas g y /a rtic Sample La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu le -a b s W95-59 15.8 39.2 5.7 26.8 6.88 2.26 7.15 1.10 6.22 1.19 3.12 0.42 2.56 0.39 tra c W95-33 13.9 35.4 5.3 25.5 6.72 2.23 7.17 1.12 6.38 1.23 3.21 0.44 2.67 0.41 t/4 6 W95-45 27.4 70.0 10.3 48.3 12.2 3.69 12.7 1.93 11.01 2.12 5.57 0.75 4.67 0.71 /1 1 W95-54 18.5 46.2 6.7 31.3 7.88 2.53 8.16 1.27 7.14 1.38 3.62 0.50 3.04 0.46 /21 9 W95-55 20.1 50.1 7.3 34.0 8.57 2.78 8.91 1.37 7.71 1.48 3.89 0.54 3.22 0.49 7 /1 W95-63 38.7 27.5 22.5 16.4 17.0 4.66 4.88 4.29 3.90 3.96 2.34 1.93 1.66 1.65 43 W95-74 12.5 31.5 4.7 22.1 5.69 1.96 6.00 0.94 5.27 1.01 2.65 0.37 2.19 0.33 35 9 W95-75 15.2 38.1 5.6 26.2 6.63 2.16 6.86 1.07 6.03 1.15 3.03 0.42 2.53 0.39 9 b W95-84 15.2 38.1 5.6 26.2 6.63 2.16 6.86 1.07 6.03 1.15 3.03 0.42 2.53 0.39 y g u e s t o n 1 thesalientsonthenorthernpartoftheisland,creatinga thatthe concentration of vents in these diffuse rift zones 4 A cRoonccaavReendoorntdhaer(nFicgo.a2s,t.bTohtteomN)W, ad3i0ff0u0semrifhtigehxt,emndossttloy hLaiksepweisresi,sttehde towvoerstteheepelostnfgl-atnekrms ogfrtohwetvholocfanthoe, tehdeifeicaest. pril 2 0 1 submarinevolcano(Standishetal.,1998).TheSEdiffuse andwestflanks,havefewsatellitevents. 9 rift extends to the flanks of Volcan Darwin (Naumann Lavas erupted from Wolf’s radial fissures are domin- et al., 2003). The NW and SE diffuse rifts support the antly large-volume a’a flows. Wolf is covered almost hypothesis of Chadwick & Howard (1991) that loading entirely with a’a, and, in our experience, has more a’a by adjacent volcanoes combined with stresses exerted lava than any other Gala´pagos volcano. This is partly by pressurized subcaldera magma bodies guide dikes becauseofthelargeproportionofunusuallysteepslopes towards those volcanoes. Each of the three sectors that thatmakeuptheupper flanksofWolfvolcano,whichis has adiffuseriftzonealso has thelowestslope gradients conducive to a’a formation. Also, flows from the radial on the volcano (Mouginis-Mark et al. 1996), indicating vents tend to be more voluminous than flows erupted 2205 JOURNALOFPETROLOGY VOLUME46 NUMBER11 NOVEMBER2005 (cid:4) .015 .005 .006 .012 .010 .015 (cid:4) 16 16 16 16 een b b P e 204b/ OI 23 52 77 73 hav 208P WH .384 .384 .383 .383 R)a / R (cid:4) 40 40 40 of s Pb nit 208204Pb/ Cornell .38366*.38439* .38563* atios(u r (cid:4) 14 14 14 14 pic Do o w 207204Pb/Pb WHOI .15557 .15558 .15542 .15541 Heliumisot nloaded fro m 207204Pb/Pb(cid:4) Cornell .1553512*.1554612* .1557312* Jollastandard. https://academ a ic (cid:4) 10 10 10 10 theL .oup.c Pb or om 204b/ OI 68 95 97 89 84f /pe R/Ra .864 .983 .904 .889 .858 .922 206bP(cid:4) WH .9188 9 .9188 .188 .188 .Ndto0511 trology/artic 206204Pb/P Cornell .18919*.18975* .18885* 43144Nd/ le-abstrac (cid:4) 14 10 12 10 10 1and t/46/1 Nd 87 1/2 143144Nd/ WHOI .0513032 .0513035 .0513034 .0513023 .0513031 orNBS9 197/1433 f 5 (cid:4) 12 12 12 12 12 24m. 99 3:IsotopicratiosofselectedWolflavas 87868786143144Sr/SrSr/SrNd/Nd(cid:4)(cid:4) CornellWHOICornell ...070270107027720513056**..07027410513049**..07031010512987 ...070271107027720513048**...070274107027520513037 .0702742 .0702762 .6Srhasbeennormalizedtoavalueof0710minedbycrushingolivinegrainsinavacuu&reportedbyBlichert-ToftWhite(2001). by guest on 14 April 2019 Table W95-25 W95-54 W95-59 W95-74 W95-75 W95-84 Sample W95-25 W95-59 W95-61 W95-74 W95-84 W95-54 W95-75 878Sr/deterData* 2206