New K–Ar ages of shield lavas from Waianae Volcano, Oahu, Hawaiian Archipelago

Ž .Journal of Volcanology and Geothermal Research 96 2000 229–242www.elsevier.comrlocaterjvolgeores

New K–Ar ages of shield lavas from Waianae Volcano, Oahu,Hawaiian Archipelago

H. Guillou a,), J. Sinton b, C. Laj a, C. Kissel a, N. Szeremeta a

a Laboratoire des Sciences du Climat et de L’EnÕironnement, CEA–CNRS, Bat. 12, 91198 Gif sur YÕette, Franceb UniÕersity of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA

Received 3 February 1999; received in revised form 27 October 1999; accepted 27 October 1999

Abstract

Ž .A geochronological study utilized the unspiked potassium–argon K–Ar technique to obtain ages from the two mainvolcanic members of the shield stage of the Waianae Volcano, HI. These new dates are further constrained using acombination of stratigraphic relationships, magnetostratigraphy and major element geochemistry. Exposed shield lavasencompass 0.85 Ma, with reliably dated tholeiitic lavas from the main shield ranging from 3.93"0.08 to 3.54"0.04 Ma,and a later shield stage ranging in age from 3.57"0.04 to 3.08"0.04 Ma. These data suggest that the total extent ofWaianae shield activity was significantly more than 1 Ma. The age of faulting in two flank zones is constrained to be about3.4 Ma. Preliminary estimates of lava accumulation rates vary from about 0.3 to 2.0 mmra; calculated rates show nosystematic variation with location in the volcano or with time. q 2000 Elsevier Science B.V. All rights reserved.

Keywords: Oahu, Hawaiian Archipelago; K–Ar geochronology; magnetic stratigraphy; APTS

1. Introduction

Age progression within the Hawaiian volcanicchain has been well documented by numerous stud-

Žies e.g., McDougall, 1979; McDougall and Duncan,1980; Clague and Dalrymple, 1987; Moore and

.Clague, 1992 , showing that the volcanoes becomeyounger toward the southeast where most of thepresent volcanic activity is located. Detailed studiesof the chronological evolution of single volcanicedifices can provide constraints on the duration ofvolcanic activity, as well as variations in volcanic

) Corresponding author. Tel.: q33-1-6982-3556; fax: q33-1-6982-3568.

Ž .E-mail address: [email protected] H. Guillou .

production rates through time. Together with geo-chemical data, detailed geochronological studies canfurther constrain the relationship of these temporalparameters to the nature of melt production related tohot spot activity.

Published ages for the Waianae volcano rangeŽbetween 3.8 and 2.9 Ma McDougall, 1963, 1964;

Funkhouser et al., 1968; Doell and Dalrymple, 1973;.Presley et al., 1997 , a period that includes the

Gauss–Gilbert magnetic reversal boundary, as wellas the Mammoth and Kaena events. Thus, the pres-ence of several relatively well-dated magnetic polar-ity reversals makes the Waianae Volcano ideal for adetailed study using combined paleomagnetic andgeochronologic methods.

Ž .Presley et al. 1997 showed that the post-shieldstage of activity at Waianae began within the Kaena

0377-0273r00r$ - see front matter q 2000 Elsevier Science B.V. All rights reserved.Ž .PII: S0377-0273 99 00153-5

( )H. Guillou et al.rJournal of Volcanology and Geothermal Research 96 2000 229–242230

reversed event and ended about 2.9 Ma, for a totalduration of approximately 150 ka. In this paper wereport results of a combined geochronological, geo-chemical and magnetostratigraphic study of the older,shield-stage lavas of Waianae Volcano. Four strati-graphic sections formed by the accumulation of nu-merous lava flows were studied. These sections in-clude some of the oldest and youngest exposedshield lavas. Two of these sections contain faultedsequences. This work provides the best estimate yetfor the duration of shield activity at Waianae Vol-cano, as well as for the range of lava productionrates during the subaerial stage of the volcanic activ-ity. The dating of the faulted sequences allows us tobracket the ages of faulting associated with collapsealong the flanks of the volcano.

2. Geological background

The Waianae volcano comprises the western andŽ .older part of the island of Oahu, Hawaii Fig. 1 , and

occurs on the relatively dry, leeward side of theisland. It includes good exposures of relatively unal-tered lavas from both shield and post-shield stages of

Ž .Hawaiian volcanism. Sinton 1986 and Presley et al.Ž .1997 divided the Waianae Volcanics into fourmembers.

The oldest exposed lavas constitute the LualualeiMember, dominated by the eruption of tholeiiticbasalts. These shield-building lavas are exposed onlyat the bases of the ridges near the western shore.Lualualei lavas were erupted during the Gilbert Re-

Ž .versed Polarity Chron GRPC . A well-developedcaldera in the vicinity of Lualualei Valley was pre-sent throughout this stage, along with one, well-de-veloped rift zone trending approximately N60W fromnear Kolekole Pass, and a less well-developed south-

Ž .ern rift zone Zbinden and Sinton, 1988 .A later shield-building stage is characterized by

increasing variability of lava compositions, includingplagioclase-phyric tholeiitic basalts, alkali olivinebasalts, and plagioclase-phyric basaltic hawaiites ofthe Kamaileunu Member of the Waianae Volcanics.Eruptions of Kamaileunu lavas occurred within thecaldera and along rift zones outside the calderaduring the Gauss Normal Polarity Chron.

In general, Lualualei lavas can be separated fromKamaileunu lavas using major-element contentsŽ .TiO , K O and total alkalis and normative compo-2 2

Ž . Ž .sition. Sinton 1986 and Zbinden and Sinton 1988showed that Kamaileunu lavas tend to have higherconcentrations of incompatible elements than do Lu-alualei samples. For example, Lualualei lavas have1.9–2.8 wt.% TiO , 0.2–0.5 wt.% K O and 2.0–2.872 2

total alkalis, whereas Kamaileunu lavas have valuesfor these elements of 2.3–3.4, 0.5–0.7 and 2.88–4.87.Lualualei lavas tend to be quartz normative, whereasKamaileunu lavas are either quartz or hypersthenenormative.

Ž .The postshield stage Presley et al., 1997 startedwith the Palehua Member, which consists of hawai-ites and rarer mugearites. This sequence is exposedon the NE and SE flanks of the volcano. A majorunconformity locally separates Palehua hawaiitesfrom the Kolekole Member Volcanics, which is thelast unit, delivering mainly basaltic products.

3. Methods

The aim of this study is to apply geochemistry,Ž .magnetostratigraphy, and potassium–argon K–Ar

dating to the definition of the main stratigraphicunits and the reconstruction of the volcanic historyof the volcano. Eighteen lava flows were studied,mainly from the northwestern and western parts ofthe volcano, where four mapped volcanic sectionswere sampled. Samples were collected in strati-

Žgraphic sequences Kaena Point, Nanakuli Valley,.Kepuhi Point and Puu Mailiili to verify the geologi-

cal significance of the obtained results and to esti-mate the accumulation rates of the lavas within theshield stage. Preliminary definition of magnetic po-larity units was carried out in the field using aportable flux-gate magnetometer. The reliability ofmagnetic field measurements was checked by furtherlaboratory analysis for some of the samples.

3.1. Geochemistry

Major-element analyses were made to estimatethe degree of alteration and to establish the rock

Ž .types of the dated lavas Table 1 . Rock chips werecleaned in an ultrasonic bath of distilled and deion-ized water prior to crushing in tungsten carbide or

( )H. Guillou et al.rJournal of Volcanology and Geothermal Research 96 2000 229–242 231

Ž .Fig. 1. Geologic map of the Waianae range after Stearns, 1939; Macdonald, 1940; Sinton, 1986; Presley et al., 1997 showing locations ofthe dated sections.

alumina swing mills. Samples were ignited for 8 h atŽ .9008C and a loss on ignition LOI was determined.

Two fused buttons and one pressed powder pelletwere prepared for each sample following procedures

modified slightly from those of Norish and HuttonŽ .1969 . Samples were analyzed using a Siemens303AS, fully automated, wavelength-dispersive, X-ray fluorescence spectrometer.

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Table 1Whole-rock analyses of lavas from WaianaeSamples were analyzed by XRF at the University of Hawaii.Fe O is total Fe reported as Fe O . LOI is loss on ignition at 9008C. NV: Nanakuli Valley. KDL: Kepuhi point dipping lavas. KAP: Kanena point. PM: Puu Mailiili. KFL:2 3 2 3

Kepuhi point flat-lying lavas.

OW174 OW175 Ka7 Ka01 OAU06 OW181 OW180 OW179 OW178 OW182 OW183 OW184 OW187 OW188 HG-1D OW185Rock type: A.B. T.B. T.B. T.B. T.B. A.B. T.B. T.B. A.B. T.B. T.B. T.B. T.B. T.B. T.B. T.B.Section: NV NV KAP KAP KAP KFL KFL KFL KFL KDL KDL KDL PM PM PM PHKMember: K L K K K K K K K K? LrK L K K K L

SiO 46.88 49.76 51.41 51.48 51.21 47.56 50.27 48.83 47.05 50.26 49.92 51.05 50.94 50.56 50.52 51.282

TiO 2.53 2.35 2.34 2.41 2.36 3.15 3.81 2.69 2.95 3.14 2.65 2.21 3.05 3.09 3.97 2.072

Al O 12.38 13.86 14.06 13.61 13.99 15.42 12.97 14.12 15.47 13.49 14.11 13.24 16.98 14.65 12.67 13.022 3

Fe O 13.70 13.04 11.70 12.00 12.04 13.85 14.34 12.19 14.09 13.79 12.08 11.87 11.19 12.10 14.09 11.962 3

MnO 0.17 0.17 0.15 0.16 0.16 0.16 0.17 0.15 0.16 0.16 0.15 0.16 0.12 0.13 0.17 0.16MgO 11.21 6.21 7.18 6.72 6.32 6.09 4.95 8.22 6.48 5.01 6.58 8.28 3.56 5.91 4.96 9.75CaO 9.62 10.56 9.89 9.71 10.19 9.84 8.70 10.03 9.73 8.92 10.05 9.66 9.09 8.67 8.22 9.58Na O 2.38 2.29 1.92 2.02 2.42 2.93 2.86 2.44 2.95 2.72 2.43 2.07 3.23 2.95 2.70 2.172

K O 0.71 0.34 0.34 0.55 0.39 0.71 0.99 0.46 0.72 0.65 0.53 0.28 0.62 0.47 0.99 0.292

P O 0.42 0.31 0.25 0.31 0.29 0.43 0.57 0.36 0.40 0.47 0.40 0.19 0.49 0.46 0.67 0.212 5

Sum 100.19 99.88 99.86 99.63 99.92 100.18 100.15 100.01 100.04 99.62 99.70 99.72 100.57 100.18 99.32 100.73LOI 0.19 0.99 0.63 0.66 0.54 0.04 0.52 0.51 0.05 1.02 0.82 0.71 1.29 1.18 0.36 0.22

CIPWHyp 3.96 22.64 25.18 23.95 18.96 6.10 20.70 20.22 2.26 21.61 22.70 27.67 16.72 22.95 21.32 31.58Ol 23.49 0.00 0.00 0.00 0.00 13.40 0.00 5.27 17.60 0.00 0.00 0.00 0.00 0.00 0.00 0.00Qz 0.00 1.52 5.01 4.98 4.46 0.00 2.12 0.00 0.00 3.00 1.30 2.89 3.09 2.19 4.27 0.50


3.2. K–Ar dating

Only rocks with minimal traces of alteration wereselected. The samples were crushed, sieved to 0.25–0.125 mm size fraction and ultrasonically washed inHC H O . Potassium and argon were measured on2 3 2

the microcrystalline groundmass, following removalof phenocrysts and xenocrysts using heavy liquids ofappropriate densities, and magnetic separations. Thisprocess improves the K yield as well as the percent-age of radiogenic argon, and removes at least somepotential sources of systematic error due to the pres-

Table 2Ž .Radiometric K–Ar dating for lava flows of Waiane volcano

Ž . y1 0 y1y1Age calculations are based on the following decay Steiger and Jager, 1977 and abundance constants:l s4.962=10 a ;¨ b

l s0.581=10y10 ay1 ; 40 KrKs1.167=10y4 molrmol.´

P: Magnetic polarity. Subscript l: laboratory magnetic polarity determinations. Subscript f: flux-gate magnetic polarity determinations.40 ) 40 ) y13Ž . Ž . ŽSample Location Height P K wt.% Ar % Ar 10 Age Age Ma

Ž . . Ž .a.s.l. m molesrg "2s Ma mean value

OW174 Nanakuli Valley 360 N 0.711"0.007 16.653 37.493 3.04"0.04f

OW174 360 N 0.711"0.007 15.148 38.391 3.11"0.04 3.08"0.03f

OW175 Nanakuli Valley 345 R 0.288"0.003 4.815 18.122 3.62"0.09f

OW175 345 R 0.288"0.003 4.936 18.239 3.65"0.08 3.64"0.06f

OW172 Nanakuli Valley 230 R 0.364"0.004 6.650 23.175 3.67"0.07f

OW172 230 R 0.364"0.004 6.172 23.738 3.76"0.07 3.71"0.05f

HN55 Navy road 220 N 0.415"0.004 8.766 22.337 3.10"0.04l

HN55 220 N 11.720 22.438 3.11"0.04 3.11"0.03l

Ka7 Kaena Point 190 N 0.375"0.004 10.564 20.746 3.19"0.04l

Ka7 190 N 0.375"0.004 9.589 20.432 3.14"0.04 3.16"0.03l

Ka01 Kaena Point 10 N 0.389"0.004 5.796 21.812 3.23"0.03l

Ka01 10 N 0.389"0.004 4.431 21.273 3.15"0.03 3.19"0.03l

OAU 06 Kaena Point 0 N 0.312"0.003 9.810 17.708 3.27"0.05f

OAU 06 0 N 0.312"0.003 6.926 17.757 3.28"0.04 3.27"0.03f

OW181 Kepuhi point 455 R 0.606"0.006 13.160 32.915 3.14"0.04f

OW181 flat-lying lavas 455 R 0.606"0.006 12.366 33.431 3.18"0.04 3.16"0.03f

OW180 Kepuhi point 260 N 0.739"0.007 16.504 40.646 3.17"0.04f

OW180 flat-lying lavas 260 N 0.739"0.007 15.611 40.846 3.18"0.04 3.18"0.03f

OW179 Kepuhi point 235 N 0.518"0.005 4.139 28.944 3.22"0.07f

OW179 flat-lying lavas 235 N 0.518"0.005 4.239 29.100 3.24"0.07 3.24"0.05f

OW178 Kepuhi point 80 N 0.603"0.006 16.044 35.050 3.35"0.04l

OW178 flat-lying lavas 80 N 0.603"0.006 17.966 34.432 3.29"0.04 3.32"0.03l

OW182 Kepuhi point 380 – 0.582"0.006 19.033 36.730 3.64"0.04OW182 dipping lavas 380 – 0.582"0.006 17.891 36.815 3.64"0.04 3.64"0.03OW183 Kepuhi point 210 – 0.417"0.004 10.890 25.792 3.56"0.05OW183 dipping lavas 210 – 0.417"0.004 11.127 25.938 3.58"0.05 3.57"0.04OW184 Kepuhi point 90 R 0.185"0.002 2.803 12.597 3.92"0.11l

OW184 dipping lavas 90 R 0.185"0.002 2.842 12.692 3.95"0.12 3.93"0.08l

OW187 Puu Maili’ili 198 R 0.626"0.006 4.440 35.522 3.24"0.07l

OW187 198 R 0.626"0.006 6.893 34.916 3.21"0.05 3.22"0.04l

OW188 Puu Maili’ili 168 R 0.421"0.004 6.128 24.317 3.33"0.06l

OW188 168 R 0.421"0.004 6.196 24.357 3.33"0.06 3.33"0.04l

HG-1D Puu Maili’ili 55 N 0.888"0.009 11.662 51.584 3.35"0.04l

HG-1D 55 N 0.888"0.009 11.778 51.598 3.35"0.04 3.35"0.03l

OW185 Puu O Hulu Kai 10 R 0.296"0.003 8.744 18.092 3.52"0.05l

OW185 10 R 0.296"0.003 9.695 18.282 3.56"0.05 3.54"0.04l


40 Ž .ence of excess Ar Laughlin et al., 1994 known tooccur in olivine and pyroxene.

K was analyzed by atomic and flame emissionspectrophotometry with a relative precision of 1%. Adescription of the unspiked technique and the instru-ment used for Ar measurements have been presented

Želsewhere Cassignol and Gillot, 1982; Cassignol et.al., 1978; Gillot and Cornette, 1986 . Argon was

extracted from 1 to 2.5 g groundmass samples byradio frequency heating induction in a high-vacuumglass line and purified with titanium sponge andSAES Zr–Al getters. Isotopic analyses were madeon Ar quantities ranging from 2=10y10 to 2=

10y11 moles, using a 1808, 6-cm radius mass spec-trometer with an accelerating potential of 620 V. Thespectrometer was operated in a semi-static mode;data were measured on a double faraday collector insets of 100 using a 1-s integration time. The sensitiv-ity of the mass spectrometer is about 5.1=10y15

molesrmV with amplifier background of 0.075 V40 Ž 9 . 36 Ž 11for Ar 10 V resistor and 5.75 mV for Ar 10

.V resistor . Procedural blanks were measured be-tween 5=10y12 and 1.2=10y11 moles with anatmospheric isotopic composition, and checked byrepeated processing of zero-age samples.

The volumetric calibration of the spike-free intro-duction line was refined by the cross calibration of

Ž .GL-O Odin, 1982; Charbit et al., 1998 , Mmhb-lŽ . Ž .Samson and Alexander, 1987 , LP-6 Odin, 1982 ,

Ž .and HD-B1 Fuhrmann et al., 1987 . This calibrationŽ .Charbit et al., 1998 allows Ar content to be deter-

Ž .mined with a precision of 0.2% "2s .

3.3. Paleomagnetism

Stepwise AF or thermal demagnetization of fivesamples per flow was conducted in the laboratory tocheck that the magnetic polarity determinations madein the field with the flux-gate magnetometer did notreflect secondary overprints. Some results of this

Ž .study are reported in Laj et al. 1999 . In general,only relatively small secondary components werepresent, which typically were easily removed afterone or two steps using temperatures less than 4008Cor AF less than 20 mT. Representative magnetization

Ž .diagrams are shown in Laj et al. 1999 . The direc-tion of the characteristic remanent magnetizationŽ .ChRM was then determined using a principal com-

ponent analysis and the Fisher’s statistic was used tocalculate the mean flow direction. In each case, afterlaboratory cleaning, all the samples from the sameflow exhibited the same polarity. The results are

Žreported in Table 2 N for normal and R forl l.reverse . The polarities determined in the field also

are reported as N or R .f f

4. Results

4.1. Chemical composition

Results of major-element analysis are reported inTable 1. LOI values range from -0.1 wt % to)1.0 wt %, reflecting the presence of low-tempera-

Ž .ture hydrous minerals clay in some samples. Thedated shield lavas from Waianae are mainly tholeiiticbasalts except for Hy-normative samples OW174,OW178 and OW181, which lie in the alkalic field on

Ž .a plot of Na OqK O vs. SiO Fig. 2 .2 2 2

Fig. 3 shows chemical data for the dated samples,along with fields for all chemically analyzed Lualu-alei and Kamaileunu shield rocks. In general, varia-tion of K O vs. SiO effectively separates most2 2

Kamaileunu from Lualualei samples, although thereis some overlap between the fields for the twomembers. It also is worth noting that subaerial alter-ation of Hawaiian volcanics can lead to loss of Kfrom the sample, so this diagram is less useful foraltered samples. Of the dated samples, only sample

Fig. 2. Na OqK O vs. SiO wt.% for Waianae shield lavas.2 2 2

Open circlessdated Lualualei member samples; filled circlessdated Kamaileunu member samples. ALK: alkalic field. TH:Tholeiitic field. Outlined fields show the compositional range ofall of the least altered, chemically analyzed Waianae shield lavas;dashed line: Lualualei field; solid line: Kamaileunu.


Fig. 3. K O vs. SiO wt.% for Waianae shield lavas. Symbols and2 2

fields are the same as in Fig. 2.

OW182 plots in a field other than that indicated byits age andror stratigraphic position.

4.2. K–Ar dating

Age determinations are reported in Table 2 alongwith the magnetic polarities. Good analytical repro-ducibility is observed for all samples. The duplicateages are within the 2s errors. The ages for theWaianae shield lavas range from 3.93"0.08 MaŽ .sample OW184, mean value to 3.08"0.03 MaŽ .sample OW174, mean value .

The three samples from the Nanakuli valley sec-tion define a range in age from 3.71"0.05 MaŽ . Ž .OW172 to 3.08"0.03 Ma OW174 . The ages ofthe Kepuhi point dipping lavas range between 3.93

Ž . Ž ."0.08 Ma OW184 and 3.57"0.04 Ma OW183 ,whereas the ages obtained for the flat-lying lavas ofKepuhi point bracket the section between 3.32"0.03

Ž . Ž .Ma OW178 and 3.16"0.03 Ma OW181 . Lavasfrom Kaena point have ages between 3.27"0.03 MaŽ . Ž .OAU06 and 3.11"0.03 Ma HN55 , and ages

Ž .range from 3.35"0.03 Ma HG-1D to 3.22"0.04Ž .Ma OW187 at Puu Mailiili.

Within each stratigraphic section, ages decreasewith height as expected, with the exception of theolder, dipping lava sequence near Kepuhi Point.Within error, samples OW182 and OW183 are thesame age, but their respective positions indicate thateither our age for OW183 is too low or that for

Ž .OW182 is too high. Chemical data see belowfavors the latter interpretation. Data for all othersamples in this study are consistent with their strati-

graphic order. However, some ages may not be fullyconsistent with other geological constraints, as dis-cussed in later sections.

4.3. Paleomagnetism

ŽIn the section at Puu Mailiili, the lower part up.110–120 m , including sample HG-1D, has normal

Žmagnetic polarity, while the upper part OW188 and.OW187 is reversed. No transitional direction was

observed between stable normal and reverse polari-ties. Ages suggest that the polarity boundary at PuuMailiili is the lower Mammoth. At Kepuhi Point, the

Ž .five dipping lavas including OW184 show reverseŽ .polarities GRPC , whereas the first 140 m of the

Ž .flat-lying section including OW178 are normal.Normal polarities are observed throughout the entire

Ž .Kaena Point section Ka01, Ka7 and HN55 . For thissection, precision on directional determinations andsecular variation analyses are described in Laj et al.Ž .1999 .

5. Discussion

5.1. Affiliation of the dated samples to a Õolcanicmember

Geological relations in combination withgeochronology, geochemistry and magnetostratigra-phy can be used to assign the dated samples unam-biguously to their appropriate volcanic member.

Ž .Based on previous studies e.g., Sinton, 1986 , Lu-alualei volcanics are low-K tholeiitic basalts, eruptedduring the GRPC; they therefore should be olderthan 3.58 Ma according to the Cande and KentŽ .1995 APTS age of the Gilbert–Gauss boundary.Kamaileunu member lavas were erupted during the

Ž .Gauss normal polarity chron GNPC , which in-Ž .cludes both the Mammoth 3.33–3.22 Ma and Kaena

Ž . Ž .3.11–3.04 Ma reversed events. Presley et al. 1997noted that the oldest post-shield Palehua lavas have

Ž .reversed magnetic polarity Kaena Event and sug-gested an age of onset of post-shield volcanism ofabout 3.06 Ma. Therefore Kamaileunu lavas shouldhave ages ranging from 3.58 to 3.06 Ma.

Reversed samples OW184, OW172, OW175 andOW185 are Lualualei, based on their chemical com-


positions, magnetic polarity and K–Ar age, takingŽ .into account analytical error Figs. 2–4 . The mag-

netic polarity of OW183 is unknown. Based on itsŽ .age and potassium content Fig. 3 this sample can

be considered to be either one of the youngestLualualei lavas or one of the oldest Kamaileunulavas. Sample OW182, for which we do not have themagnetic polarity, plots clearly in the Kamaileunufield on Figs. 2 and 3. Although its age suggests thatit is Lualualei, this age is not consistent with stratig-

Ž .raphy Table 2 . The reliability of this age determina-tion will be discussed along with others in the fol-lowing sections.

ŽAll the samples with normal polarity younger.than the Gilbert–Gauss boundary are part of the

Kamaileunu member. This includes samples OW174,HN55, Ka7, Ka01, OAU06, OW180, OW179,OW178 and HG-1D. Kamaileunu samples with re-versed polarity include OW187, OW188, andOW181.

5.2. Correlation of the K–Ar ages to the APTS

Analytical errors from the K–Ar study are givenin Table 2. However, it is well known that real errors

Žcan be greater than analytical errors Dalrymple and.Lanphere, 1969 if the rocks have not remained

closed to K and Ar since formation. Moreover, acalculated age greater than the real age can result if

Ž40 .the sample contains excess Ar, i.e., Ar in additionto that which has been produced by the decay of 40 Ksince the time of formation of the rock, or has lost Kduring subaerial weathering. Alternatively, underesti-mated ages can result if the sample has gained 40 Kandror lost 40Ar ). Although the removal of phe-nocrysts in this study should reduce the potential forinherited argon, alteration effects are more difficultto assess and the technique we used in this study isbased on the assumptions that at t , time of forma-0

tion of the rock, the 40Arr36Ar ratio in the samplewas equivalent to the modern 40Arr36Ar atmosphericratio and that the rocks have remained closed to Kand Ar since t . The potential for analytical prob-0

lems associated with K–Ar dating is especially prob-lematic in studies of shield lavas of Hawaiian volca-noes because of the generally low K contents inshield tholeiites.

One test of the reliability of our calculated ages isto compare them to the astronomical polarity time

Ž .scale APTS . In contrast to the radio-isotopic

Ž .Fig. 4. Graph of new K–Ar data. The magnetic time scale is after Cande and Kent 1995 . Circles correspond to data summarized by DoellŽ .and Dalrymple 1973 .


timescale, which is based on K–Ar and Ar–Ar dat-ing studies, APTS is calibrated independently usingsolar insulation periodicities observed in seawater

ŽO-isotopic curves Schackelton et al., 1990; Hilgen,.1991 . Thus the availability of magnetic polarity

determinations for samples in this study allows us tobetter constrain the reliability of our calculated ages.

The ages of most samples determined in thisstudy agree within analytical error with their mag-

Ž .netic polarity Table 2, Fig. 4 . Although the meanages for eight of the eighteen dated samples do notagree with their magnetic polarity or other strati-graphical information, only three of these disagreeby more than the analytical errors. For example,reversed sample OW 185 can be reconciled with itsmagnetic polarity if it is older than the Gauss–Gil-bert transition, consistent with its chemical composi-tion indicating that it is Lualualei. Although themean K–Ar age of 3.54"0.04 Ma is slightlyyounger than the APTS age of the Gauss–Gilbert

Žboundary 3.58 Ma; Hilgen, 1991; Cande and Kent,.1995 , it is very similar to the one proposed by

Ž .Cande and Kent 1992 which is 3.55 Ma. In anycase, the error on this age allows it to be as old as3.58 Ma. Similarly, although the mean ages forsamples OW178, OW179, and OW174 are in con-flict with their magnetic polarities, all are consistentwithin errors if OW 178 is older than 3.33 Ma,OW179 is younger than 3.22 Ma, and OW174 isolder than 3.11 Ma.

Although these new data represent a substantialimprovement to the earlier work of Doell and Dal-

Ž .rymple 1973 , there are, however, still discrepanciesthat suggest that the calculated ages for some sam-ples are less accurate than implied by the analyticalprecision. Sample OW182 is chemically Kamaileunuand stratigraphically higher than sample OW183.Thus, it must be younger than our determination of3.64"0.03 Ma.

Reversed sample OW181 yielded an age of 3.16"0.03. Thus it must have formed either during theKaena or Mammoth events. Presently available evi-dence does not permit us to unequivocally distin-guish between these two possibilities, but its location

Žfavors the younger period. Sample OW174 mean.age 3.08"0.03 Ma has a normal polarity but a

radiometric age corresponding to the Kaena reverseevent. Although the analytical error on the age of

OW174 permits it to be as young as 3.05 Ma, nearthe upper boundary of the Kaena event, this agewould put it within the post-shield Palehua Member,lavas of which are uniformly hawaiite in composi-

Ž .tion Presley et al., 1997 . Thus, given the normalmagnetic polarity of OW174, this basaltic sampleshould be older than 3.11 Ma.

The measured age for sample OAU06 also doesnot agree with its magnetic polarity within error ofthe age analysis. In a detailed paleomagnetic study of

Ž .the Kaena Point section by Laj et al. 1999 , all lavaswere determined to be normally magnetized. TheKamaileunu–Palehua boundary, which occurs withinthe Kaena reversed section, also was not encounteredat Kaena Point. Thus, the most likely age for thisentire section is within the normal polarity chron

Ž .between the upper Mammoth transition 3.22 MaŽ .and the lower Kaena transition 3.11 Ma . If so, the

K–Ar age of OAU06 must be too old and its trueage less than 3.22 Ma. Although the mean age ofHN55 is too young for its magnetic polarity, theanalytical error allows this sample also to haveformed prior to the Kaena event. An alternativeexplanation is that the true age of OAU06 is greaterthan 3.33 Ma and that Mammoth polarity lavas werenot emplaced in this location distant from the centerof Waianae Volcano.

5.3. Causes of age discrepancies

As mentioned above, in some cases it is clear thatthe real errors in the age determinations must begreater than the analytical errors. Some ages appear

Žto be too old samples OW179, OW181, OW182,.and OAU06 , whereas others are underestimated

Ž .OW174, OW178, and OW185 . Errors can arisefrom incomplete extraction of argon during analysis,from extraneous argon, or from element migrationdue to weathering. 40Ar–39Ar incremental heatingexperiments have shown significant differences be-tween measured initial 40Ar–36Ar ratios and the mod-ern atmospheric 40Ar–36Ar ratio in feldspars and

Žpyroxenes Lanphere and Dalrymple, 1976; Zeitler.and Fitzgerald, 1986 . In zero-age ocean island

basalts, olivine phenocrysts can have 40Arr36Ar rang-Ž .ing from 300 to 1000 Kaneoka et al., 1983 . Be-

cause we have been able to reproduce ages fromseparate groundmass aliquots of individual samples,


incomplete extraction of argon is unlikely. The re-moval of phenocrysts and xenocrysts should haveeliminated this potential source of excess argon.Therefore, other sources of excess argon and elementmigrations during weathering are the most likelysources of error in our age determinations.

During solidification, incomplete degassing ofmagmatic argon can occur, which represents anothersource of excess 40Ar. For example, magmatic40Arr36Ar ratios in some zero-age Hawaiian lavas

Ž .range from 300 to 450 Allegre et al., 1983 . Thisprocess may be responsible for the overestimatedages of samples OW179, OW181, and OAU06; thisexplanation is preferred over minor loss of K duringsubaerial weathering because these samples all have

Ž .relatively low LOI -0.55% . The LOI valueŽ .1.02% of OW182 indicates that it is moderatelyaltered and so its apparent old age could be due

Ž .either to element migration K loss during weather-ing or to excess 40Ar ).

Underestimation of ages may be explained by40Ar ) loss resulting from devitrification of glass or

Ž .other alteration Renne et al., 1993 . Very smallamounts of K-rich glass or its alteration products canexert a significant influence on a rock’s K budget,and hence, affect the calculated age, as proposed by

Ž .Sharp and et al. 1996 to explain younger apparentages of some flows from Mauna Kea. These pro-cesses may be responsible for the young apparentages of samples OW174, OW178, and OW185.

5.4. Ages of Waianae Õolcanic actiÕity

Previous studies determined the ages of exposedsub-aerial Waianae lavas to range from 3.8 to 2.9 MaŽMcDougall, 1963, 1964; Funkhouser et al., 1968;

.Doell and Dalrymple, 1973; Presley et al., 1997 .The oldest age obtained in our study is 3.93"0.08

ŽMa lowest flow of the dipping lavas located near.Kepuhi point . The boundary between the Lualualei

and Kamaileunu Members is the Gauss–GilbertŽboundary at 3.55–3.58 Ma Hilgen, 1991; Cande and

.Kent, 1992; 1995 . The youngest Lualualei sampleŽdated in this study is from Puu o Hulu Kai 3.54"

.0.04 Ma .Ž .Presley et al. 1997 showed that the oldest post-

shield lavas are from the type locality of the Kaenareversed event, and field evidence using a flux-gate

magnetometer confirms this relationship elsewherein the volcano. They proposed an age of 3.06 for theboundary between the shield and post-shield stagesŽ .Kamaileunu–Palehua boundary . The oldest dated

ŽKamaileunu sample in our study is HG-1D 3.35".0.03 Ma . The youngest probably is the reversely

magnetized sample OW181, if this sample owes itspolarity to eruption during Kaena time; althoughsamples HN55 and OW174 yield younger ages, theirnormal magnetic polarity suggests eruption prior tothe Kaena event.

Taken together, available geologic, geomagneticand geochronologic evidence suggests that the end ofshield volcanism at Waianae volcano occurred withinthe Kaena event, approximately 3.08"0.04 Ma. Thisgives the total extent of the Kamaileunu Member tobe 0.45–0.50 Ma, and the total dated range of Wa-ianae shield volcanism to be 0.85 Ma. Owing to

Ž .volcano subsidence e.g. Moore, 1987 and burial byyounger flows, the oldest lavas of the shield stageare not presently exposed in the Waianae Range.

Ž .Moore 1987 estimates as much as 2–4 km ofsubsidence for most of the older volcanoes of theHawaiian Chain. As such, the beginning of Lualualeivolcanism and the total duration of this stage areunknown. Nevertheless, the total dated range of 0.85Ma for the presently exposed portion above sea levelsuggests that total Waianae shield volcanism proba-bly lasted considerably more than 1 Ma.

Based on radiometric dating of Loihi seamountand new volume estimates for the sizes of Hawaiian

Ž . Ž .volcanoes Garcia et al., 1995 , Guillou et al. 1997suggested the overall duration of a typical Hawaiianvolcano to be ;1.4 Ma. This total estimate forshield volcanism is considerably longer than some

Žprevious ones e.g., 0.65–1.0 Ma; Moore and Clague,.1992; Lipman, 1995; DePaolo and Stolper, 1996 . If

it applies to Waianae, then the beginning of Waianaeactivity may have been as early as 4.5 Ma ago.

Ž .Following the model of Guillou et al. 1997 a250-ka-long Waianae preshield would have endedabout 4.24 Ma and the Lualualei main shield phasewould have lasted about 700 ka. Data in this papershows that the late-shield Kamaileunu Member lasted450 ka. Waianae post-shield volcanism lasted ap-

Ž .proximately 150 ka. Presley et al., 1997 .The above arguments suggest that the total life

span of the Waianae volcano may have been on the


order of 1.5 Ma. No other Hawaiian volcano hasbeen dated as extensively as Waianae, but publishedages for exposed subaerial lavas of the Koolau Vol-cano span 900 ka and those for Kauai about 1.5 MaŽ .Langenheim and Clague, 1987 . These results indi-cate that volcanic activity lasting more than 1 Mamay be a common feature of Hawaiian volcanoes.

The duration of approximately 0.5 Ma for thelater shield, Kamaileunu Member, indicates that Wa-ianae had a prolonged period of transitional volcan-ism leading to the post-shield stage of activity. Tran-sitional and alkalic basalts first appear in the Ka-maileunu Member, as well as a distinctive suite ofhigh silica, intracaldera lavas and dikes associatedwith the Mauna Kuwale Rhyodacite Flow. SintonŽ .1986 suggested that the age of this flow is greaterthan 3.2 Ma. At least the upper flows that make up

Ž .Puu Mailiili Table 2 can be correlated with thoseunconformably overlying the Mauna Kuwale Rhyo-dacite Flow on the adjacent ridge to the north. Fieldmeasurements suggest transitional to reversed mag-netic polarities at Mauna Kuwale. Taken together thebest age for the Mauna Kuwale Rhyodacite probablyis close to the lower Mammoth polarity boundary orabout 3.3 Ma.

5.5. Age of faulting

A prominent saddle in the ridge between Lualu-alei and Nanakuli valleys near Puu Heleakala marksthe location of a normal fault separating Lualualeilavas to the south and Kamaileunu lavas to the north;the latter are ponded against the north-facing faultscarp. The youngest unequivocally faulted lava isOW175 so the faulting must be younger than 3.64"

0.04 Ma. The oldest ponded flow is OW174. Al-though we obtained an age of 3.08"0.04 Ma forthis sample, its magnetic polarity indicates that itprobably is older than 3.11 Ma. Thus the age offaulting in this area is 3.38"0.27 Ma.

A similar approach can be used to bracket the ageof the east-facing normal fault near Kepuhi Point.

ŽHowever, because the age of OW182 is suspect see. Ž .above , we use the age of OW183 3.57"0.04 as

the youngest reliable age for the faulted lavas. Sam-Ž .ple OW179 3.24"0.05 Ma is the oldest flow

which ponded against the fault scarp. These resultsindicate that this faulting must have occurred about

3.41"0.17 Ma. It is notable that the age bracketsfor the two dated faults in this study are equivalentwithin uncertainty. These two faults represent flankstructures that were present in the late shield stage ofWaianae activity.

5.6. LaÕa accumulation rates

Information about the rate of accumulation of lavaduring Lualualei time can be obtained from the

Žsections at Kepuhi Point and Puu Heleakala Nanakuli.Valley . The 115 m between samples OW172 andŽ .OW175 Nanakuli section apparently accumulated

in less than 180 ka, yielding a minimum accumula-tion rate of 0.6 mmra. The mean ages for samplesOW172 and OW175 suggest an average accumula-tion rate of 1.6 mmra, but the maximum rate cannotbe calculated, given the errors on the age determina-

Ž .tions Fig. 5 . The 120 m thick lava section betweenOW183 and OW184 at Kepuhi Point accumulated in360"120 ka, at an average rate of 0.38"0.12mmra, using the maximum and minimum age deter-minations for the section. These two late Lualualeisections are approximately equidistant from the cen-ter of Waianae Volcano, located near the back of

ŽLualualei Valley Sinton, 1986; Zbinden and Sinton,.1988 .

The flat-lying, 143-m-thick Kamaileunu section atPuu Mailiili accumulated inside the Waianae calderaover approximately 130"70 ka, yielding a rate of1.6"0.9 mmra. Estimation of accumulation rate forthe younger section at Kepuhi Point is complicatedby uncertainties in some of the ages and the possiblepresence of unconformities in the section. Neverthe-less the 180 m between OW178 and OW180 appearsto have formed in about 140"60 ka for an averagerate of 1.6"0.7 mmra, essentially identical to thatat Puu Mailiili. If the entire, 220-m-thick section atKaena Point all formed within the 110-ka intervalbetween the Kaena and Mammoth events, this wouldyield a minimum accumulation rate of 2.0 mmra.This location is the most distal from the volcanocenter of any exposure in Waianae, yet it possiblyyields the highest accumulation rate. It is difficult toassess the validity of this result. The alternativesuggestion, that the absence of reversed polarityrocks at Kaena Point reflects hiatuses in the section,cannot be precluded, which would lower the accumu-


Fig. 5. Ages vs. stratigraphic heights showing lava accumulationrates. Mean values are reported in the text, whereas, minimum andmaximum values are given on the figure. Grey triangles aresamples from Kaena point which do not have a coherent age withthe magnetic polarity.

lation rate to values closer to those determined else-where in the volcano.

Taken together, the dated sections of this studysuggest that accumulation rates throughout the shieldstage varied from about 0.3–2.0 mmra. These pre-liminary results generally correspond to those esti-

Ž .mated for Mauna Kea Sharp et al., 1996 and LoihiŽ .Guillou et al., 1997 , as well as that deduced from

Ž .the model of DePaolo and Stolper 1996 , for the lasthalf of a volcano’s lifetime. Our limited data suggestthat local variations within the shield stage are greaterthan any systematic variations that might be ex-pected to occur over time or with distance from thevolcano center.

6. Conclusions

The unspiked K–Ar technique has been used tosuccessfully date shield lavas from four differentstratigraphic sequences of the Waianae volcano. Theirages range from 3.93"0.08 to 3.08"0.03 Ma. Thelowermost exposed, strongly tholeiitic portion of the

Ž .volcano Lualualei member: main shield stage rangesin age from 3.93"0.08 to 3.54"0.02 Ma; the

Župper transitional part of the volcano Kamaileunu.member: late shield stage ranges from ;3.5 to

3.08"0.03 Ma. These age ranges do not include thesubsided part of the main shield stage. Thus the totalduration of Waianae shield volcanism must be muchgreater than the combined age range of presently

Ž .exposed shield lavas 0.85 Ma . Previous estimatesof 0.65 to 1.0 Ma for the duration of Hawaiian shield

Ž .volcanism Moore and Clague, 1992; Lipman, 1995clearly do not apply to Waianae. The age of faultingdated in this study has a mean value of ;3.4 Ma.The age of the Mauna Kuwale Rhyodacite Flow islikely to be approximately 3.3 Ma.

Acknowledgements

Andrea Kaawaloa prepared most of the samplesfor which chemical analyses are reported in thispaper, and Cliff Todd helped with the XRF analyses.Critical comments by David Clague were greatlyappreciated and helpful in improving the manuscript.Nathalie Max made most of the K analysis. Theauthors also want to acknowledge Jean FrancoisTannau for his technical support. This work has beenfinancially supported by the French CEA and

ŽCNRSrINSU LSCE contribution No. 0311; SOEST.contribution No. 4891 .

References

Allegre, C.J., Staudacher, T., Sarda, P., Kurz, M., 1983. Con-straints on evolution of the earth’s mantle from rare gassystematic. Nature 303, 762–766.

Cande, S.C., Kent, D.V., 1992. A new geomagnetic polaritytimescale for the late Cretaceous and Cenozoic. J. Geophys.Res. 97, 13917–13951.


Cande, S.C., Kent, D.V., 1995. Revised calibration of the geo-magnetic polarity timescale for the late Cretaceous and Ceno-zoic. J. Geophys. Res. 100, 6093–6095.

Cassignol, C., Gillot, P.Y., 1982. Numerical Dating in Stratigra-phy. Wiley, Chichester, 159–179.

Cassignol, C., Cornette, Y., David, B., Gillot, P.Y., 1978. Tech-nologie potassium–argon. C.E.N., Saclay. Rapp. CEA R-4802,37 pp.

Charbit, S., Guillou, H., Turpin, L., 1998. Cross calibration ofK–Ar standard minerals using an unspiked Ar measurementtechnique. Chem. Geol. 150, 147–159.

Clague, D.A., Dalrymple, G.B., 1987. The Hawaiian–Emperorvolcanic chain: Part I. Geologic evolution. U.S. Geol. Surv.Prof. Paper 1350, 5–54.

Dalrymple, G.B., Lanphere, M.A., 1969. Potassium–argon dating.Ž .In: Woodford, A.O., Gilluly, J. Eds. , Principles, Techniques

and Applications to Geochronology. Freeman, San Francisco,251 pp.

DePaolo, D.J., Stolper, E.M., 1996. Models of Hawaiian volcanogrowth and plume structure: implications of results from theHawaii Scientific Drilling Project. J. Geophys. Res. Lett. 101,11643–11654.

Doell, R.R., Dalrymple, G.B., 1973. Potassium–argon ages andpaleomagnetism of the Waianae and Koolau Volcanic series,Oahu, Hawaii. Geol. Soc. Am. Bull. 84, 1217–1242.

Fuhrmann, U., Lippolt, H., Hess, J.C., 1987. HD-B1 biotitereference material for K–Ar chronometry. Chem. Geol. 66,41–51.

Funkhouser, J.G., Barnes, I.L., Naughton, J.J., 1968. The determi-nation of a series of ages of Hawaiian volcanoes by thepotassium–argon method. Pac. Sci. 22, 369–372.

Garcia, M.O., Hulsebosch, T.P., Rhodes, J.M., 1995. Olivine-richsubmarine basalts from the southwest rift zone of Mauna LoaVolcano: implications for magmatic processes and geochemi-cal evolution. Am. Geophys. Union, Geophys. Monogr. 92,219–239.

Gillot, P.Y., Conette, Y., 1986. The Cassignol technique for K–Ardating, precision and accuracy: examples from the late Pleis-tocene to recent volcanics from southern Italy. Chem. Geol.59, 205–222.

Guillou, H., Garcia, M.O., Turpin, L., 1997. Unspiked K–Ardating of young volcanic rocks from Loihi and Pitcairn hotspot seamounts. J. Volcanol. Geothermal. Res. 78, 239–249.

Hilgen, F.J., 1991. Astronomical calibration of Gauss to Matuyamasapropels in the Mediterranean and implication for the Geo-magnetic Polarity Time Scale. Earth Planet. Sci. Lett. 104,226–244.

Kaneoka, I., Takaoka, N., Clague, D.A., 1983. Noble gas system-atics for coexisting glass and olivine crystals in basalts anddunite xenoliths from Loihi seamount. Earth Planet. Sci. Lett.66, 427–437.

Laj, C., Guillou, H., Szeremeta, N., Robert Coe, R.S., 1999.´ ´ ´Geomagnetic paleosecular variation at Hawaii around 3 Ma

Ž .BP from a sequence of 107 lava flows at Kaena Point Oahu .Earth Planet. Sci. Lett. 170, 365–376.

Langenheim, V.A.M., Clague, D.A., 1987. The Hawaiian–Em-peror volcanic chain: Part II. Stratigraphic framework of vol-

canic rocks of the Hawaiian Islands. Volcanism in Hawaii,Vol. 1. U.S. Geol. Surv. Prof. Paper 1350, 55–84.

Lanphere, M.A., Dalrymple, G.B., 1976. Identification of excess40Ar by the 40Arr39Ar age spectrum technique. Earth Planet.Sci. Lett. 32, 141–148.

Laughlin, A.W., Poths, J., Healey, H., Reneau, S., WoldeGabriel,G., 1994. Dating of quaternary basalts using the 3He and 14Cmethods with implications for excess 40Ar. Geology 22, 135–138.

Lipman, P.W., 1995. Declining growth of Mauna Loa during thelast 100,000 years: rates of lava accumulation vs. gravitationalsubsidence. Am. Geophys. Union, Geophys. Monogr. 92, 45–80.

Macdonald, G.A., 1940. Petrography of the Waiianae range,Ž .Oahu. In: Stearns, H.T. Ed. ,Supplement to Geology and

Groundwater Resources of the island of Oahu, Hawaii. Hawai,Div. Hydrogr. Bull. 5pp. 61–91.

McDougall, I., 1963. Potassium–Argon ages from western Oahu,Hawaii. Nature 197, 344–345.

McDougall, I., 1964. Potassium–Argon ages from lavas of theHawaiian islands. Geol. Soc. Am. Bull. 75, 107–128.

McDougall, I., 1979. Age of shield building volcanism and linearmigration of volcanism in the Hawaiian Island chain. EarthPlanet. Sci. Lett. 3246, 31–42.

McDougall, I., Duncan, R.A., 1980. Linear volcanic chains —recording plate motions? Tectonophysics 63, 275–295.

Moore, J.G., 1987. Subsidence of the Hawaiian Ridge. U.S. Geol.Surv. Prof. Paper 1350, 85–100.

Moore, J.G., Clague, D.A., 1992. Volcano growth and evolutionof the island of Hawaii. Geol. Soc. Am. Bull. 104, 1471–1484.

Norish, K., Hutton, J.T., 1969. An accurate X-ray spectrographicmethod for the analysis of a wide range of geological samples.Geochim. Cosmochim. Acta 33, 431–441.

Odin, G.S., 1982. Numerical Dating in Stratigraphy. Wiley,Chichester, 2 vols., 1094 pp.

Presley, T.K, Sinton, J.M., Pringle, M., 1997. Postshield volcan-ism and catastrophic erosion of the Waianae volcano, Oahu,Hawaii. Bull. Volcanol. 58, 597–616.

Renne, P.R., Walter, R.C., Verosub, K.L, Swetzer, M., Aronson,Ž .J.L., 1993. New data from Hadar Ethiopia support orbitally

tuned time scale to 3.3 million years ago. Geophys. Res. Lett.20, 1067–1070.

Samson, S.D., Alexander, E.C. Jr., 1987. Calibration of the intral-aboratory 40Arr39Ar dating standard MMhb-1. Chem. Geol. 6,27–34.

Schackelton, N.J, Berger, A., Peltier, W.R., 1990. An alternativeastronomical calibration of the lower Pleistocene timescalebased on ODP site 677. Trans. R. Soc. Edinburgh: Earth Sci.81, 251–261.

Sharp, W.D, Turrin, B.D., Renne, P.R., 1996. 40Arr39Ar andK–Ar dating of lavas from the Hilo 1-km corehole, HawaiiScientific Drilling Project. J. Geophys. Res. 101, 11607–11616.

Sinton, J., 1986. Revision of stratigraphic nomenclature of Wa-ianae volcano, Oahu, Hawaii. U.S. Geol. Surv. Bull. 1775 A,9–15.

Stearns, H.T., 1939. Geologic map and guide of the island of


Ž .Oahu, Hawaii geologic map enclosed . Hawaii, Div. Hydrogr.Bull. 2, 75 pp.

Steiger, R.H., Jager, E., 1977. Convention on the use of decay¨constants in geo- and cosmochronology. Earth Planet. Sci.Lett. 36, 359–362.

Zbinden, E.A., Sinton, J., 1988. Dikes and the petrology ofWaianae Volcano, Oahu. J. Geophys. Res. 93, 14856–14866.

Zeitler, P.K., Fitzgerald, J.D., 1986. Saddle-shaped 40Arr39Arage spectra from young, microstructurally complex potassiumfeldspars. Geochim. Cosmochim. Acta 50, 1185–1199.

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New K–Ar ages of shield lavas from Waianae Volcano, Oahu, Hawaiian Archipelago