The Gilsá excursion and the Matuyama/Brunhes transition recorded in 40Ar/39Ar dated lavas from Lanai and Maui, Hawaiian Islands

Geophys. J. Int. (2009) 179, 43–58 doi: 10.1111/j.1365-246X.2009.04264.x

GJI

Geo

mag

netism

,ro

ckm

agne

tism

and

pala

eom

agne

tism

The Gilsa excursion and the Matuyama/Brunhes transition recordedin 40Ar/39Ar dated lavas from Lanai and Maui, Hawaiian Islands

R. Leonhardt,1 M. McWilliams,2 F. Heider3 and H. C. Soffel41Department for Applied Geosciences and Geophysics, Montanuniversitat, Leoben, Austria. E-mail: [email protected] & Environmental Sciences, Stanford University, Stanford, CA, USA3Infineon Technologies AG, Villach, Austria4Department for Earth and Environmental Sciences, Ludwig-Maximilians-Universitat, Munich, Germany

Accepted 2009 May 20. Received 2009 April 30; in original form 2007 December 13

S U M M A R YDirectional results, Thellier-type palaeointensity determinations and Ar/Ar ages are presentedfrom volcanic units of Pleistocene age from the Hawaiian islands of Maui and Lanai. Twenty-nine non-contiguous lava flows were sampled on Lanai. The lava flows formed during thelate Matuyama polarity chron about 1.6 Ma and recorded the Gilsa geomagnetic polarityexcursion. The obtained ages of 1.6 Ma for the Lanai lavas are significantly older than agespreviously obtained for this island. These new ages are, however, in agreement with the ageprogression of the Hawaiian hotspot. The palaeomagnetic record over the sampled successionis characterized by reversed and intermediate directions. palaeointensities are generally verylow, about half the present-day field intensity, dropping to values of ∼5 μT during transitionalfield states. Transitional virtual geomagnetic poles (VGPs) from Lanai are situated first near thewest coast of South America and then switch to offshore western Australia. Normal polarityis never reached in the sampled succession. Transitional VGPs located close to Australiaaccompanied by relatively low palaeointensities are found in most records of short geomagneticexcursions during the Matuyama polarity chron (e.g. the Cobb Mountain subchron, the Punaruevent and the Matuyama/Brunhes precursor) suggesting very similar physical processes likelyrelated to dipolar dominance during the onset of these excursions and influences of lowermantle heterogeneities. Approximately 800 kyr after the Gilsa excursion, lava flows on Mauirecorded the last reversal, the Matuyama/Brunhes transition. Fourteen lava flows were sampledwhich recorded the pre- and post-transitional behaviour of the Earth’s magnetic field. Thegeomagnetic field intensity is low prior to the reversal, approximately 8 μT, and increasesstrongly afterwards up to ∼63 μT. These values of about twice the present field intensity ofHawaii after the transition emphasize a strong asymmetry between pre- and post-transitionalfields, which is particularly strong in the region of Hawaii.

Key words: Geomagnetic excursions; Palaeointensity; Reversals: process, timescale,magnetostratigraphy.

1 I N T RO D U C T I O N

Palaeomagnetic investigations on Hawaiian lava flows began al-ready in the early sixties with the seminal studies of Doell & Cox(1961, 1965). Numerous palaeomagnetic results were publishedsince those early days on volcanic sequences from the Hawaiianislands, focusing on a wide range of different geomagnetic ques-tions and ages of sampled units (e.g. Doell 1972a,b; Bogue & Coe1984; Baksi et al. 1992; Mankinen & Champion 1993; Herrero-Bervera & Valet 1999; Bogue 2001; Laj et al. 2002; Teanby et al.2002; Herrero-Bervera & Valet 2005). The high-extrusion ratesof the Hawaiian shield volcanoes represent excellent conditions toinvestigate the transitional field behaviour during geomagnetic re-versals and excursions. Studies of the transitional field behaviour

were conducted on several different reversals recorded in Hawaiianlavas, starting with the last reversal, the Matuyama/Brunhes tran-sition (Baksi et al. 1992; Coe et al. 2004b) up to reversals dur-ing the Gauss chron (Herrero-Bervera & Coe 1999) and theGilbert chron (Bogue & Coe 1984). An important potential ofvolcanic records of the past geomagnetic field is the possibil-ity to analyse the full palaeomagentic vector, that is, inclina-tion, declination and absolute palaeointensity. For some of thesetransitional records, in particular the early Pliocene Kauai tran-sition, palaeointensity determinations were conducted (Bogue &Coe 1984; Bogue 2001). Local palaeomagnetic records of direc-tional and intensity variation during or close to transitional ge-omagnetic field states provide essential information regarding aglobal interpretation of the reversal processes and, therefore, the

C© 2009 The Authors 43Journal compilation C© 2009 RAS

44 R. Leonhardt et al.

understanding of the mechanisms within the geodynamo. Particu-larly, on the Hawaiian islands, not only full geomagnetic reversalsbut also other transitional and non-transitional volcanic records wereinvestigated using palaeointensity determinations. Such palaeoin-tensity studies on Hawaiian lavas are now covering age ranges fromthe most recent lavas (Coe et al. 1978; Mankinen & Champion1993; Yamamoto et al. 2003) to the Brunhes polarity chron (Laj &Kissel 1999; Laj et al. 2002; Teanby et al. 2002) up to the Pliocenelavas on Hawaii (Coe et al. 1984; Laj et al. 2000; Bogue 2001;Herrero-Bervera & Valet 2005) with a diminishing amount of gapswithin the data set.

Here, we present volcanic records from two Hawaiian islands,Lanai and Maui, where full vector measurements were conducted.The Gilsa event (Wensink 1964; McDougall & Wensink 1966;Watkins et al. 1975) was sampled in a reconnaissance study onLanai. It is still debated whether this event, which happened1.61 Ma (Udagawa et al. 1999), should be referred to as a globalnormal polarity subchron or an excursion of the geomagnetic field(Clement & Kent 1987). Our Lanai record adds to a small collec-tion of globally distributed records, and provides for the first time,absolute palaeointensity information for the Gilsa excursion.

On the island of Maui, the last full reversal of the Earth’s magneticfield, the Matuyama/Brunhes transition was sampled in a volcanicsequence approximately 10 km south of the records of Baksi et al.(1992) and Coe et al. (2004b). Pre- and post-transitional directionsaccompanied by palaeointensity determinations were obtained fromthis sequence.

2 G E O L O G I C A L S E T T I N G

The volcanic rocks of Lanai originate from a single shield volcano(Fig. 1a). They represent only the shield stage and consist of tholei-

SettlementsRift zoneSediments

)alakaelaH(iuaMtsaEiuaMtseWianaL

Hana Volcanics (<0.05 Ma)

Kula Volcanics (0.88-0.41 Ma)

Honomanu Basalt (~0.8 Ma)Shield basalts (1.4-0.8 Ma)

Lanai City

Kaumalapau

Kapukaloa

203°00’ 203°06’

20°54’

20°48’

a) Lanai

Wailuku

Hana

Kaupo

Keawakapu

Lahaina

Pahihi Gulch

Pali-Trail

21°00’

20°30’’00°402’03°302

b) Maui

rejuvenated stage

post-shield stage

shield stage

Lahaina Volcanics (<0.7 Ma)

Honolua Volcanics

Wailuku Basalt (1.6-1.3 Ma)

(~1.2 Ma)

Sampling locations

Hawaiian islands

MauiLanai

Figure 1. Geological sketch map of Maui and Lanai (Hawaiian Islands) according to Langenheim & Clague (1987). Filled circles indicate sampling locationson both islands. The given ages of the volcanic series are the oldest respectively youngest K/Ar determinations according to Naughton et al. (1980).

itic basalts (West et al. 1992) which formed presumably between 1.2and 1.7 Myr (Bonhommet et al. 1977, this study). Younger ages of0.7–0.8 Ma were obtained in Maunalei Gulch on the north coast ofLanai (Naughton et al. 1980). These ages are, however, affected bylarge uncertainties due to the small amount of radiogenic elements(Naughton et al. 1980). Normally magnetized lavas were found nei-ther in our study, nor by Herrero-Bervera et al. (2000), who sampledeight sites from different places on Lanai, indicating volcanic ac-tivity occurred exclusively during the Matuyama polarity Chron.In a reconnaissance effort we took palaeomagnetic samples from29 lava flows in the Kaumalapau gulch and along the road towardsKaumalapau harbour. The lava flows dip 5◦ in the upper part and8◦ in the lower portion to the west. Lavas are predominantly of thePahoehoe type. Only a few AA flows are observed. No evidenceof block tilting, rotations or major unconformities was observedalong the sampled profile. In the lower part of the profile (flowsL-K2 to L-K11) there are between three and ten unsampled lavaflows between each site. For flows L-K13 to L-K15 and L-K17 toL-K19, two to four flows were identified between the sites. In theupper part of the section (L-K22 to L-K28) adjacent lavas weresampled within Kaumalapau gulch. The stratigraphic relationshipbetween site L-K11 and 12, L-K15 and 16, L-K21 and 22, as wellas the stratigraphic position of sites L-K1 and L-K29 is not de-ducible from field observations since large parts of the sequenceare covered by debris. Sampling distance/altitude and average lavadip correlations already suggest a possible recurrence of sampledsuccessions. palaeomagnetic results support a repetition of parts ofthe sequence which will be discussed more precisely later. A singlewollsack weathered lava flow was sampled close to the volcanic riftin the northcentral part of Lanai.

The island of Maui consists of two shield volcanoes, the youngerHaleakala volcano (East Maui) and the older West Maui volcano

C© 2009 The Authors, GJI, 179, 43–58

Journal compilation C© 2009 RAS

Palaeomagnetism of Maui and Lanai 45

Figure 2. Stratigraphy of the two profiles sampled in the Pahihi Gulch,Maui. The suggested correlation between the two profiles is indicated byarrows. Also shown is the polarity of the flows.

(Fig. 1b). Three major units are defined on the West Maui vol-cano (Stearns & Macdonald 1942): the Wailuku series (shieldstage), the Honolua volcanic series (post-shield stage) and theLahaina series (rejuvenated stage). Palaeomagnetic samples fromtwo lava flows were taken from the ∼1.6 Myr old (Naughton et al.1980) Wailuku series. Three major units are also identified on theHaleakala volcano: the Honomanu, Kula and Hana series formingthe shield, post-shield and rejuvenated stage, respectively (Stearns &Macdonald 1942). Samples were taken from the 0.41 to 0.88 Myrold Kula series (Naughton et al. 1980). Two profiles were sampledin the Pahihi Gulch on the southern side of the Haleakala volcano,which cuts through the stratigraphically lower part of the Kula series(Fig. 2). Profile M-PGA was sampled approximately 1 km north ofKaupo road within the gulch. 150 m north of M-PGA, closer to theHaleakala caldera and the supposed extrusion centre of the lavas,profile M-PGB was sampled. Despite the limited distance betweenthe two profiles a direct flow-to-flow correlation is complicated. Thelavas cannot be followed due to debris coverage and erosion withinthe gulch. Nevertheless, the presence of a prominent ash layer belowflows M-PGA7 of profile A and M-PGB6 of profile B (Fig. 2), thesimilar composition and physical appearance of flow and ash layer,an occurrence in agreement with the overall average dip of flowsin this area, and finally the almost identical palaeomagnetic resultssuggest a correlation marker. Based solely on palaeomagnetic data,a correlation of other lava flows of M-PGA to profile M-PGB issuggested as well (Fig. 2). These lavas are characterized by almostidentical palaeomagnetic direction and palaeointensities, indicatinga formation during a very short period of time. At first instance,however, both profiles will be analysed independently.

The outcrops of profile B are partly covered by debris. Gaps arethus present in this succession. AA lavas (Fig. 2) are characterizedby a massive interior part and a well defined scoria on the upper flowboundary. Vesicular flows also show a thin scoria on the upper part

of the individual flow. The composition of the ash layers is domi-nated by fine particles with larger (Ø50 cm) lava blocks and bombswithin the fine grained matrix. Three larger blocks of the ash layersuperimposed on M-PGB3 were sampled and palaeomagneticallyanalysed. All three blocks revealed completely different palaeomag-netic directions, indicating a magnetization before deposition. Theflow between M-PGB6 and M-PGB7 was not accessible for drilling.Fluxgate measurements, however, indicate normal polarity.

The thickness of the sampled lava flows from Maui and Lanairanges between 0.4 and 3 m. All sampled lavas appear to be in situ.Therefore, no tectonic corrections were applied for analysing thesamples. Sampling was conducted using a portable, water cooleddrill. Whenever possible cores were drilled in the central part ofthe flow with horizontal spacings of at least 1 m between differentsamples. In order to avoid lightning strike remagnetized lavas thedeflection of the compass needle was checked.

3 PA L A E O - A N D RO C K M A G N E T I CR E S U LT S

3.1 Rock magnetic investigations and ore microscopy

At least one sample from every flow was used for a set of standardrock magnetic measurements. IRM-acquisition, backfield curves,hysteresis loops at room temperature and thermomagnetic curves(Bmax = 500 mT, T max = 700 ◦C) were measured for each of thesesamples using a Variable Field Translation Balance (VFTB). A ver-tical profile of eleven evenly spaced samples from the bottom to thetop of flow M-PGB3 indicates the presence of significant rock mag-netic differences depending on the vertical position of the sample.Different rock magnetic properties are also observed for horizon-tally spaced samples from single lavas. Therefore, all rock magneticmeasurements can be termed representative only for the sample incharge and not for the whole flow. Strong-field thermomagneticcurves [Ms(T )] point to the presence of several different magneticphases in most samples from both islands. Wasp waisted hysteresiscurves are common, particularly in the Lanai tholeiites. For thesereasons, domain state and grain size analysis according to Day et al.(1977) is highly ambiguous and we refrain from interpreting suchplots. Three characteristic T C-ranges are observed by Ms(T )-curvesin all investigated samples. T Cs between 500 and 580 ◦C are presentin all specimens from Maui and Lanai. During thermal demagne-tization similar high unblocking temperatures bearing a character-istic remanent magnetization are found, indicating that this hightemperature phase did not exclusively arise from alteration duringthermomagnetic curve measurements as inferable from the coolingcurve of Fig. 3(c). Ore microscopy showed that cubic idiomorphicto subidomorphic titanomagnetite grains are present. By emphasiz-ing strongly magnetized parts of individual grains using a magneticcolloid, exsolution lamellae can be identified (Fig. 3a). Intergrowthstructure and configuration of lamellae point to a formation of thehigh T C phase during high-temperature oxidation, most likely dur-ing primary cooling of the lavas. Specimens with a single high-T C

are, however, rather rare in the collection. Specimens from eightlavas from Lanai and six lavas from Maui revealed such charac-teristics. Most other specimens showed an additional T C-range of80–250 ◦C. These low T C’s are interpreted as resulting from pre-dominantly unexsolved titanomagnetite grains and, possibly, Fe-richhemoilmenite grains (Fig. 3b), mostly already accompanied by mi-nor maghemitization. Advanced maghemitization leading either toadditional T C’s (Figs 3b and c) or exclusive T C’s between 300 and

C© 2009 The Authors, GJI, 179, 43–58



Figure 3. Thermomagnetic curves and light microscopic pictures of specimens from Maui [(a) M-PGA1-5, (b) M-PGB1-5] and Lanai [(c) L-K26-5]. Solidlines indicate heating curves, dashed lines show cooling curves of strong-field thermomagnetic measurements. For ore microscopic observations the sampleswere covered with magnetic colloid to emphasize strongly magnetized parts. Titanomagnetites of various grain sizes and different oxidation states, as well ashemoilmenites are found in all lavas from Lanai and Maui. Idiomorphic and subidomorphic titanomagnetites with ilmenite lamellae are the dominant magneticmineral in single high-TC specimens (a). Unexsolved titanomagnetites are present in most samples, accompanied by grains of differently advanced grade ofalteration (b and c). Titanomagnetites/Titanomaghemites with cruciform and dendritic structures (c) are only present in tholeiites from Lanai.

420 ◦C is observed in almost 45 per cent of the samples from Lanaiand 25 per cent of the Maui collection. By ore microscopic observa-tion of colloid covered samples, the formation of titanomaghemiteduring low-temperature oxidation is observed particularly at therim of individual grains and along cracks within grains (Figs 3band c). A few samples showing more than one T C were subjected tocontinuous thermal demagnetization of the natural remanent mag-netization (NRM). A reversible increase of magnetization duringheating, with a respective decrease during cooling was found insome of these samples when conducting a heating/cooling cycleabove the lower T C and below the higher T C. This signature isinterpreted as being caused by magnetic interaction leading to par-tial self-reversal of magnetization (Heller & Petersen 1982; Krasa2003). We found that this does not bias the directional informationof the high temperature component. With respect to palaeointen-sity determinations, however, partial self-reversal due to secondaryminerals would bias the experiment (Coe 1974).

Ms(T ) measurements already revealed magnetomineralogicalchanges during heating/cooling cycles (Fig. 3c). Such alterationsare of particular interest for palaeointensity determinations usingThellier-type techniques, since these involve numerous laboratory

heating/cooling cycles in zero magnetic field, as well as in non-zerofields. Magnetomineralogical changes during laboratory treatmentaffect the capacity of samples to acquire partial thermoremanentmagnetizations (pTRM) and may lead to failures of the experi-ment. In order to quantify such alteration mechanisms and analysetheir possible effects on our intensity experiments, alternating field(AF) demagnetization of an ARM (150 mT AC, 50 μT DC) in roomtemperature and after heating to 200, 400 and 550 ◦C according toLeonhardt et al. (2000) were performed on 11 samples showingdifferent rock magnetic characteristics, as well as different alter-ation characteristics during absolute palaeointensity determination(Fig. 4). Non-altering samples show a linear relationship with aslope of 1 in these plots (Fig. 4a). Fig. 4(b) shows a sample withsignificant deviations from this line after heating to 400 ◦C. Magne-tomineralogical changes led to a strong increase of the low coerciv-ity magnetic fraction, whereas the high coercivity fraction decreasesslightly. After heating to 550 ◦C the high coercivity fraction furtherdecreased. The low coercivity fraction also decreased with respectto the 400 ◦C step. The increase of the low coercivity fraction athigh temperature is of particular interest for palaeointensity deter-minations, as it can be interpreted in a way that it leads to a more

C© 2009 The Authors, GJI, 179, 43–58



0 50 100 150 200 250

ARM [mA/m] (at 20°C)

0

50

100

150

200

250

AR

M[m

A/m

](a

fterheatin

g/c

oolin

gcy

cle

tox°

C)

x = 200°Cx = 400°Cx = 550°C

0 50 100 150 200 250

ARM [mA/m] (at 20°C)

0

50

100

150

200

250

0 mT

20 mT

20 mT

40 mT70 mT

0 mT

60 mT

a) b)

Figure 4. AF demagnetizations of an ARM at room temperature versus demagnetizations of ARM after heating to 200, 400 and 550 ◦C for single high-TC

sample M-PGA5-7 (a) with similar characteristics as Fig. 3(a) and M-PGB1-4 (b) which has comparable characteristics to Fig. 3(b). Linear behaviour withslope 1.0 indicates that no alteration occurred during the experiment (a). Magnetomineralogical changes lead to a deviation from this line (b).

multidomain (MD) like behaviour of samples at intermediate to hightemperatures, which may bias the interpretation of high temperaturesegments.

3.2 Palaeodirectional analysis

Measurements and demagnetization of the NRM were performed inthe magnetically shielded room at the palaeomagnetic laboratory ofthe University of Munich in Niederlippach. Remanence measure-ments were carried out using a Molspin spinner magnetometer and,for weakly magnetized samples, with a 2G cryogenic magnetome-ter. On average, one half of the samples was treated thermally up to600 ◦C and the other half with stepwise AF demagnetization up to150 mT. For the majority of the lava flows thermal and AF demag-netization were equally effective for determining the characteristicremanent magnetization (ChRM) of the samples. The demagne-tization data were analysed using principal component analysis.Typical demagnetization diagrams are shown in Fig. 5. A primarycharacteristic component could be unambiguously identified in93 per cent of the samples. Viscous overprints yielding the present-day magnetic field direction were observed, but these could usuallybe removed at demagnetization steps below 200 ◦C or 20 mT, re-spectively. Secondary components up to 400 ◦C were also found ina few samples, likely related to the presence of titanomaghemites.Despite our precautions during sampling, a few samples from Mauiwere affected by lightning strike remagnetizations which were thenidentified by differences between magnetic and sun compass orien-tation and during laboratory treatment by high NRM intensities andAF demagnetization characteristics. These samples and a few otherswith unstable directions were excluded from further analysis. Fornine samples a stable end point analysis was not suitable, whereforethe great circle technique according to McFadden & McElhinny(1988) was applied. The mean directions for each lava flow werecalculated using Fisher (1953) statistics (Table 1).

Successive lavas were tested whether they recorded indepen-dent states of the geomagnetic field. In order to quantify the inde-pendency of successive directions we used the F-distribution test(e.g. Butler 1992). The probability to which successive flows areindependent was calculated and for values less than 95 per centbetween flows, the lavas are assumed to have recorded the samegeomagnetic field. These flows were then combined to a directionalgroup DG (Table 1). This purely directional approach is supportedby similar intensities within DG M-PGA1-6. For the other DGs

this assumption is only based on directional results, for which thegrouping is not completely unambiguous. Calculation started fromthe lowest and, therefore, oldest flow.

Intermediate directions, where the difference between the Earth’srotation axis and the virtual geomagnetic pole (VGP) latitude isgreater than 35◦, are observed in 12 flows from Lanai. It is foundthat these intermediate directions fall into two specific groups. Thefirst group, hereinafter transitional field state 1, shows directionsof inclination (I) ∼ 14◦, declination (D) ∼ 125◦, the other group,transitional field state 2, I � −34◦, D � 233◦. Herrero-Berveraet al. (2000) also sampled two sites close to Kaumalapali Harbour(sites 6 and 7) which show very similar field directions to thelavas investigated here. Site 7 of Herrero-Bervera et al. (2000) alsorecorded an intermediate direction corresponding to transitionalfield state 2.

Two polarities are identified in profile M-PGB in the Pahihi Gulchof Maui. The lower three flows record reverse directions, the upperfour flows normal directions of the geomagnetic field. Accordingto the radiometric ages of the Kula series, this field reversal corre-sponds to the Matuyama/Brunhes transition. Previously, records ofthis transition with several intermediate directions were found in theKula volcanics within the caldera of the Haleakala volcano (Baksiet al. 1992; Coe et al. 2004b). In the sampled profiles presentedhere, however, no transitional directions are found. This is verylikely linked to the significant distance to the eruption centre andthe relatively sporadic eruption frequency of post-shield volcanics.

3.3 Palaeointensity determination

Thellier-type palaeointensity determinations were only conductedon samples, which yield the mean characteristic remanence direc-tion of the flow. Furthermore, we selected samples, which appearto be most suitable according to rock magnetic and palaeomag-netic measurements, in particular, samples showing evidence forpredominant high temperature oxidation during primary cooling ofthe lavas, minimal alteration during thermal treatment, low viscosityand high magnetic stability. Samples showing partial self-reversal ormixtures of different magnetic minerals were discarded. Palaeoin-tensity determination of samples showing an increase of low co-ercivity during the thermal ARM experiments (Fig. 4b) were alsonot analysed, neither corrected nor uncorrected for alteration. Alto-gether 107 samples from 26 lavas were chosen for palaeointensitydeterminations. Successful results were obtained from 43 samples

C© 2009 The Authors, GJI, 179, 43–58



L-K18-2B L-K21-2A

L-KK1-4D

M-PGB1-3A

M-PGA5-4C

)b)a

)d)c

)f)e

10mT

30mT

M-LP2-1B5mT

20mT

50mT

5mT

20mT50mT

60mT

200°C

Up,W

Up,W

N

Up,W

Up,W

Up,W

N

N

N

N

N

Up,W

450°C

600°C

440°C

300°C

100°C

560°C

100°C

300°C

560°C

440°C

-1000

-2000

-3000

2000 4000

-200-400

-10000

-4000

-1000-2000

-6000

Figure 5. Orthogonal projections of demagnetization data from Lanai and Maui. Scales on the axis are given in mA m−1. Open symbols correspond toprojections on the vertical plane, solid symbols to the projection on the horizontal plane.

of 13 lavas. 90 per cent of the measurements were performed inan argon atmosphere on minicores with a diameter of 5 mm. Theother samples were of standard inch-size and were treated in air,yielding a similar success rate and similar results as the minicores.All palaeointensity determinations were conducted in a MMTD20thermal demagnetizer, with a laboratory-built sample holder forminicores. These minicores were taken unoriented from the lowerpart of individual drill cores and the primary character of the di-rection was ascertained by the demagnetization of sister specimensfrom the same drill core. Due to the smallness of the specimensthe orientation in the sample holder along the x- and y-axis withinthe cryogenic magnetometer the results were affected with slightlyhigher deviations, leading to a more scattered declination informa-tion than for inch specimens. Pilot samples (e.g. Fig. 6d) were notoriented within the x–y plane, since the previously used sampleholder for the cryogenic magnetometer did not allow an accuratex–y orientation. Therefore, the declination varies strongly for them.The acquisition of pTRM along the sample’s z-axis, however, wasaccurate within 1◦, wherefore vector subtraction for the analysisof minicore determinations can be performed exclusively along thez-axis. The major advantage of using minicores stems from a re-duced time for each heating cycle and the use of a larger collectionof samples within one measurement run which are all centred in

the furnace, guaranteeing a small temperature gradient. Laboratoryfields of 20–35 μT, applied during heating and cooling, were usedfor all measurements. Field accuracy is 0.1 μT. All palaeointen-sity determinations were analysed using the ThellierTool software(Leonhardt et al. 2004a) by applying the default criteria of thissoftware.

Pilot samples were measured using two modifications of the Thel-lier method, MT1 and MT2 (see (Leonhardt et al. 2004a) for adetailed description of these modifications). MT1 refers to experi-ments with demagnetization at a given temperature prior to acquisi-tion of a pTRM at the same temperature. The inverse treatment, in-field measurement before zero-field measurement is termed MT2.MT2 experiments enable one to identify components of magneti-zation acquired during the field-on step which are not removed bythermal demagnetization to the same temperature, either due to al-teration or MD-tails. Most palaeointensity determinations were per-formed with the modified Thellier-technique MT4, which is a zero-field first method, and besides, the commonly used pTRM checkadditionally incorporates additivity checks (Krasa et al. 2003) andpTRM-tail checks (Riisager & Riisager 2001) evaluated with re-spect to the directional difference between applied field and NRMaccording to Leonhardt et al. (2004b). pTRM checks were con-ducted for all methods ‘in-field’ after the demagnetization step. The

C© 2009 The Authors, GJI, 179, 43–58



Table 1. Palaeodirectional results from Lanai and Maui.

Site n/N(Ngc) Dec Inc k α95 VGPLong VGPLat P np/N p Fw ± Dw Age ± 2σ

(◦) (◦) (◦) (◦) (◦) (μT) (Ma)

LanaiKaumalapau Gulch (N: 20.79◦, E: 203.02◦)L-K1 9/5 130.1 −47.3 143 6.4 313.0 −44.3 IL-K2 6/6 156.4 −50.6 456 3.1 323.3 −66.6 RL-K3 6/6 174.6 −60.6 162 5.3 11.6 −67.9 R 4/4 19.5 ± 0.7L-K4 9/7 178.9 −45.3 50 8.6 322.5 −84.2 R

L-K5 8/6 190.7 −59.0 162 5.3 44.7 −68.1 RL-K6 6/6(2) 187.9 −61.6 55 9.5 38.0 −67.1 R

DG: L-K5-6 14/12(2) 189.4 −60.3 103 4.3 42.2 −68.1 RL-K7 6/6 128.9 14.9 541 2.9 268.9 −32.8 IL-K8 6/6 122.6 10.3 625 2.7 274.9 −27.6 IL-K9 7/7 186.0 −14.6 82 6.7 182.3 −77.1 RL-K10 6/6(1) 235.3 −26.5 61 8.8 112.8 −40.0 IL-K11 7/7 166.2 −5.2 69 7.3 241.3 −67.4 R 6/3 14.0 ± 0.8 1.55 ± 0.25L-K12 6/6 122.3 13.9 1314 1.8 273.1 −26.9 I 2/1 6.9L-K13 6/6(5) 128.1 12.4 101 7.9 271.6 −30.8 IL-K14 6/5 206.7 −36.8 249 4.9 107.9 −64.1 RL-K15 6/6 224.1 −45.5 287 4.0 94.7 −49.7 I 1.60 ± 0.08L-K16 6/6 122.3 17.9 146 5.6 271.0 −25.9 I 4/3 13.7 ± 0.7L-K17 6/6 246.3 −24.8 500 3.0 108.4 −26.6 I 1/1 6.4L-K18 6/6(1) 239.5 −25.7 241 4.4 110.0 −33.0 I

L-K19 7/7 159.0 −6.7 41 9.5 252.5 −63.7 RL-K20 6/6 161.4 −10.5 76 7.7 254.9 −66.2 R

DG: L-K19-20 13/13 160.1 −8.5 54 5.7 255.2 −64.5 RL-K21 6/6 184.1 −39.6 1414 1.8 85.3 −85.8 RL-K22 6/6 238.9 −39.4 83 7.4 100.8 −35.9 IL-K23 6/6 222.2 −54.9 292 3.9 82.2 −50.0 IL-K24 6/6 214.4 −52.2 869 2.3 84.3 −57.2 R 6/4 4.6 ± 0.8L-K25 6/6 193.8 −52.8 281 4.0 62.6 −72.2 R

L-K26 6/6 176.4 −48.0 57 9.0 2.1 −81.1 RL-K27 7/6 175.2 −53.4 558 2.8 10.6 −76.4 R

DG: L-K26-27 13/12 175.8 −50.7 99 4.4 4.5 −78.7 RL-K28 6/6 159.6 −23.4 217 4.6 271.5 −68.6 RL-K29 6/6 174.2 −17.0 387 3.4 228.7 −76.7 RKapukaloa (N: 20.867◦. E: 203.011◦)L-KK1 4/4 190.1 −37.6 139 7.8 109.6 −80.6 R

MauiWest Maui, Lahaina-Pali (N: 20.791◦. E: 203.437◦)M-LP1 3/3 165.0 −33.7 594 5.1 286.6 −75.7 R 6/5 18.3 ± 0.3M-LP2 3/3 185.6 −22.9 344 6.7 171.4 −79.6 REast Maui, Pahihi Gulch, Profile A (N: 20.639◦. E: 203.801◦)

M-PGA1 8/8 346.8 30.0 79 6.3 96.1 76.7 N 13/5 30.1 ± 1.3M-PGA2 6/5 354.2 26.2 138 6.5 63.8 81.2 NM-PGA3 6/6 353.8 26.8 149 5.5 67.2 81.2 NM-PGA4 6/6 354.0 30.4 110 6.4 77.8 82.9 NM-PGA5 8/8 350.8 27.5 75 6.4 80.7 79.4 N 7/6 26.6 ± 1.1M-PGA6 6/6 352.8 33.6 166 5.2 96.6 82.8 N

DG: M-PGA1-6 40/39 351.7 29.2 98 2.3 82.6 80.6 N 23/11 28.4 ± 1.0M-PGA7 7/6 6.0 18.7 134 5.8 355.3 77.5 N 0.70 ± 0.03

results and statistical parameters for successful determinations arelisted in Table 2. The calculation of a weighted standard devia-tion (SDw) is strictly speaking mathematically not correct since theweight is not determined according to the theory of errors. Nev-ertheless, the quality differences of palaeointensity determinationsand, therefore, the applied quality related weighting of palaeointen-sity encourage us to weight the standard deviation as well. Mostspecimens are from separately oriented drill cores. For some sites,several specimens were measured from the same drill core, for ex-ample, M-PGA5-2 and M-PGA5-2D (Table 2) where specimen 2is a minicore taken, as always, from the lowermost part of the drill

core and specimen 2-D is an inch sample from the same core. Forcalculation of the mean palaeointensity of these sites, the multiplemeasurements of one drill core were averaged before calculatingan overall site mean from independent drill core results. Some ex-amples of accepted palaeointensity determinations are shown inFig. 6. Twenty-two samples of the collection were analysed usingcorrections for magnetomineralogical changes (Valet et al. 1996;Leonhardt et al. 2003). This method uses the cumulative differ-ence of pTRM checks for correcting alteration which affects block-ing/unblocking temperatures below the heating step of the check.An important prerequisite for applying this method is a proven

C© 2009 The Authors, GJI, 179, 43–58



Table 1. (Continued.)

Site n/N(Ngc) Dec Inc k α95 VGPLong VGPLat P np/N p Fw ± Dw Age ± 2σ

(◦) (◦) (◦) (◦) (◦) (μT) (Ma)

East Maui, Pahihi Gulch, Profile B (N: 20.640◦. E: 203.799◦)M-PGB1 14/9 179.9 −28.7 141 4.3 204.8 −84.7 RM-PGB2 13/11 199.8 −44.6 165 3.6 92.8 −71.0 R 7/2 8.1 ± 1.2M-PGB3 21/19 190.0 −44.7 129 3.0 80.1 −79.2 R 3/2 7.3 ± 0.1

M-PGB4 8/8 347.4 31.1 37 9.2 98.0 77.5 NDG: M-PGB-4,PGA1-6 48/47 351.0 29.5 77 2.4 85.8 80.2 N 24/11 28.4 ± 1.0M-PGB5 6/6 356.6 25.0 92 7.0 47.7 81.8 N 6/5 40.4 ± 1.5

M-PGB6 6/5 4.7 14.1 66 9.5 4.5 75.8 NDG: M-PGB-6,PGA-7 13/11 5.4 16.6 93 4.7 359.7 76.8 N 0.70 ± 0.03M-PGB7 5/5 343.0 33.5 132 6.7 108.4 73.8 N 4/2 63.0 ± 0.6

Notes: Shown are site mean inclinations and declinations, as well as the precision parameter k and α∫

95 for individual sites and directional groups DG. n/Ndenotes the number of samples treated (n) versus the number of samples used (N) for calculating the site mean direction. The number of samples analysedwith great circles (Ngc) is given in brackets. Also shown are the VGP coordinates, the polarity P (R: reversed, N: normal, and I: intermediate). Directionswere considered to represent intermediate polarity when the difference between the Earth’s rotation axis and the VGP latitude was greater than 35◦. Attempted(np) to successful (np) palaeointensity determinations, as well as weighted mean palaeointensity (Fw) and associated standard deviation (SDw) are given. Thelast column contains the average isochron age plus the 2σ standard deviation. Individual units contained in directional groups are indented and printed italic.Site locations were determined by GPS (WGS84).

absence of MD remanence. In addition to curved diagrams, MDeffects also led to biased pTRM checks (Leonhardt et al. 2004b),whose differences to the pTRM value are used for correcting mag-netomineralogical changes. In case of our experiments, the absenceof MD remanence was tested by pTRM-tail checks and additivitychecks. If correction is successful, additivity checks should fall onthe associated pTRM values, and therefore provide a meaningful testregarding the quality of the correction, as they also indicate any on-going alteration between successive heating/cooling cycles betweenpTRM check and additivity check as well as whether the alterationproducts obey Thelliers’ law of additivity. If check correction wasapplied, the class in Table 2 was extended by a superscripted star.Check corrected and non-corrected determinations yield similarresults for the lavas.

4 40A r / 39A r A G E D E T E R M I NAT I O N

The 40Ar/39Ar analyses were performed at Stanford University withanalytical procedures identical to those published in Hacker et al.(1996). Irradiation took place at the Oregon State University TRIGAreactor. We used Taylor Creek sanidine (USGS standard 85G003;Duffield & Dalrymple 1990) with an assigned age of 27.92 ±0.17 Ma as a neutron fluence monitor. The grains were heated un-der UHV conditions in a double-vacuum Staudacher-type resistancefurnace. The evolved gas was purified during extraction by SAESST-172 and ST-101 getters and a stainless steel cold finger and wasanalysed on a MAP 216 mass spectrometer fitted with a Baur-Signerion source and a Johnston MM1 multiplier. Analyses were correctedfor system blanks and instrumental mass discrimination using theprogram EyeSoreCon written by B.R. Hacker. Uncertainties for agesquoted in this paper are 2σ standard deviation.

The isochron ages are preferred over the weighted mean plateauages. They comprise estimates of analytical precision and internaldisturbance of the sample without making an assumption about thetrapped argon content. Results are summarized in Fig. 7 and Table 3.

Altogether, results from three lava flows were obtained, two lavasfrom Lanai and one flow from Maui. The age for the two flows fromLanai are well defined and give an average age of ≈1.6 Ma for theLanai sequence. This age is significantly older than previous resultsfrom Bonhommet et al. (1977), which were obtained from six dif-

ferent sites, three of them at our sampling sites close to Kaumalapauharbour and reveal an average isochron K/Ar age of 1.20 ± 0.04 Mafor the Lanai lavas. These K/Ar ages were recalculated using mod-ern decay standards (Steiger & Jager 1977). The relatively youngages previously obtained for Lanai led to an anomaly within the ageprogression of the Hawaiian hotspot (Clague & Dalrymple 1987).The here obtained age of ≈1.6 Ma, however, is in agreement withthe distance to the present-day hotspot.

5 D I S C U S S I O N

5.1 Lanai

The directional record of the lavas sampled at Kaumalapau, Lanai,is characterized by the recurrence of two similar intermediate di-rections. A detailed map with the sampling locations of all sitesis shown in Fig. 8. Boxes within this map enclose sampling siteswhere lavas are identified as successive, however, not superimposedflows. The directional evolution, associated palaeointensities and40Ar/39Ar ages for each of these four successions is also shownin Fig. 8. The striking recurrence of very similar field variationsbetween those sections is interpreted as an indication for repeatedsampling of the same geomagnetic event. This interpretation is prin-cipally supported by the radiometric ages of sites L-K15 and L-K11(Fig. 8). We have, however, to admit that due to the overlappinguncertainties of these ages, this age progression is not statisticallysignificant. Geological field evidence for the palaeomagnetic in-terpretation is poor. The relationship between sampling positionrelative to the caldera and the average dip of lavas towards the sea(8◦ in the lower part, 4◦ in the upper) further indicates that all sitesare located at a similar stratigraphic level. Nevertheless, we cannotexplicitly exclude that the transitional states are adopted succes-sively several times. For further discussion we prefer to establishfive directional units, consisting of pre-transitional lavas (Unit 1: L-K3,4,5,6), transitional state 1 (Unit 2: L-K7,8,12,13,16), in-betweentransitional state 1 and state 2 (Unit 3: L-K9), transitional state 2(Unit 4: L-K10,14,15,17,18,22) and Unit 5 (L-K11,19,20,28) cov-ering lavas exposed after transitional state 2. The VGPs for groupsand individual lavas are shown in Fig. 9. The direction of transitionalfield state 1 results in a VGP position west of South America and

C© 2009 The Authors, GJI, 179, 43–58



)b)a

)d)c

100°C350°C

475°C

550°C

1.0

0.5

0.0

)m/

Am

87

53

*(M

RN

0.15.00.0

pTRM (* 5981 mA/m)

L-K3-3

18.4 ± 0.4 μT

)m/

Am

20

85

*(M

RN

100°C

350°C

475°C

550°C

1.0

0.5

0.00.15.00.0

pTRM (* 7991 mA/m)

M-PGB7-1

62.7 ± 2.8 μT

)m/

Am

73

12

* (M

RN

pTRM (* 4737 mA/m)

100°C 300°C

400°C

490°C

550°C

1.0

0.5

0.00.15.00.0

L-K11-1

15.0 ± 0.3 μT

5%

0%

-5%

(t*) [%]

200 400 600Temp. [°C]

100°C250°C

380°C

480°C

570°C

1.0

0.5

0.0

)m/

Am

42

85

* (M

RN

0.15.00.0

pTRM (* 6408 mA/m)

M-PGA5-3

26.4 ± 0.8 μT

5%

0%

-5%

(t*) [%]

200 400 600Temp. [°C]

)f)e

200°C

400°C

490°C

580°C

1.0

0.5

0.0

)m/

Am

77

8*(

MR

N

0.15.00.0

pTRM (* 5736 mA/m)

L-K24-5C

3.1 ± 0.2 μT

400°C

490°C

570°C

1.0

0.5

0.0

)m/

Am

00

65

*(M

RN

0.15.00.0

pTRM (* 4379 mA/m)

M-PGB1-10

30.0 ± 1.0 μT X,H

-Y,-Z100°C

350°C

475°C

550°C

-2000

X,H

-Y,-Z

250°C480°C

570°C

3000

X,H

-Y,-Z200°C

400°C

550°C

X,H

-Y,-Z

475°C550°C

-2000

X,H

-Y,-Z

490°C

2000 4000

X,H

-Y,-Z200°C

400°C

490°C

580°C

200

200 400Temp. [°C]

5%

0%

-5%600

(t*) [%]

Figure 6. NRM/pTRM diagrams for six samples from Maui and Lanai. The straight line segment is well defined and covers on average 69 per cent of theNRM for the collection. Triangles indicate pTRM checks and squares denote additivity checks. In case of MT4 experiments a inset on the lower left of theplots shows the directional corrected measure of the tail, normalized to the true NRM (Leonhardt et al. 2004b). The directional demagnetization behaviouris shown in the orthogonal projection in the upper right of each plot. Relatively large directional deviations, not related to field components, are present inpilot minicore samples (a and d). Figs (e) and (f) represent two NRM/pTRM diagrams after applying corrections for magnetomineralogical changes (Valetet al. 1996; Leonhardt et al. 2003). The additivity checks fit the corrected pTRM values, indicating that MD remanence does not bias the determination andalteration correction was successful.

transitional field state 2 gives a VGP position west of Australia.The path between unit 4 and 5 is defined by lavas L-K23 to L-K27.The intermediate VGP positions near Australia are very close tothe location of the preferred VGP cluster of geomagnetic reversalsproposed by Hoffman (1992, 1996) and within preferred longitudi-

nal transitional VGP bands (Laj et al. 1991). The South Americacluster as proposed by Hoffman (1992), however, is further east thantransitional field state 1.

The strong variations of directions appear to happen ‘fast’,within only a few lava flows. Between each of the sites L-K6 to

C© 2009 The Authors, GJI, 179, 43–58



Table 2. Palaeointensity results from Hawaii.

Site n/N Specimen Type Tmin Tmax Np f g q w Class H ± SD Fw ± SDw

(◦C) (◦C) (μT) (μT)

Lanai, KaumalapauL-K3 4/4 L-K3-1 MT4 200 600 14 0.94 0.85 35.8 10.3 B* 21.0 ± 0.5 19.5 ± 0.7

L-K3-2 MT4 100 600 15 1.00 0.89 8.1 2.2 B* 19.5 ± 2.2L-K3-3 MT2 200 550 9 0.78 0.76 30.8 11.6 B 18.4 ± 0.4L-K3-4 MT4 410 540 5 0.55 0.65 3.8 2.2 B 17.9 ± 1.7

L-K11 6/3 L-K11-1 MT4 200 600 14 0.88 0.89 36.8 10.6 A* 15.0 ± 0.3 14.0 ± 0.8L-K11-2Di MT1 300 520 7 0.48 0.77 4.1 1.8 A* 13.3 ± 1.2

L-K11-5 MT2 350 600 9 0.69 0.85 19.8 7.5 B* 12.7 ± 0.4L-K12 4/1 L-K12-1 MT2 500 600 5 0.69 0.56 7.6 4.4 A 6.9 ± 0.4 6.9L-K16 4/3 L-K16-2 MT4 200 460 8 0.53 0.85 4.8 2.0 B 14.3 ± 1.3 13.7 ± 0.7

L-K16-3 MT4 200 480 8 0.63 0.85 4.0 1.6 B 14.7 ± 2.0L-K16-4 MT4 100 480 9 0.63 0.85 7.5 2.8 B 12.6 ± 0.9

L-K17 4/1 L-K17-4 MT2 500 600 5 0.55 0.60 5.3 3.0 A 6.4 ± 0.4 6.4L-K24 6/4 L-K24-2 MT4 200 570 13 0.99 0.89 6.9 2.1 B 4.0 ± 0.5 4.6 ± 0.8

L-K24-3 MT4 100 600 14 0.93 0.83 15.5 4.5 B* 4.2 ± 0.2L-K24-5 MT2 500 600 5 0.62 0.71 8.9 5.1 A* 7.2 ± 0.4

{ }L-K24-5Ci MT1 430 580 6 0.68 0.75 9.6 4.8 A 3.1 ± 0.2

Maui, Lahaina-PaliM-LP1 6/5 M-LP1-1 MT4 400 510 5 0.45 0.73 5.7 3.3 A 18.9 ± 1.1 18.3 ± 0.3

M-LP1-2Ai MT2 400 525 5 0.55 0.65 4.7 2.7 A* 17.9 ± 1.4⎧⎨⎩ M-LP1-2 MT1 435 600 7 0.90 0.67 15.7 7.0 B* 17.6 ± 0.7

⎫⎬⎭M-LP1-2D MT2 475 575 5 0.79 0.63 19.9 11.5 B* 18.8 ± 0.5

M-LP1-3 MT4 100 530 11 0.79 0.73 5.1 1.7 B 18.0 ± 2.0Maui, Pahihi Gulch

M-PGA1 13/5 M-PGA1-10 MT4 250 590 12 0.94 0.82 23.3 7.4 B 30.0 ± 1.0 30.1 ± 1.3M-PGA1-12 MT4 250 600 11 0.82 0.70 13.4 4.5 B* 27.1 ± 1.2M-PGA1-13 MT4 200 600 12 0.89 0.86 20.7 6.6 A* 33.5 ± 1.2M-PGA1-5 MT2 350 500 5 0.40 0.67 6.3 3.6 B 27.4 ± 1.2

M-PGA1-7Ci MT1 200 580 10 0.79 0.73 4.3 1.5 B 32.0 ± 4.3M-PGA5 7/6 M-PGA5-2 MT2 500 600 5 0.63 0.54 4.7 2.7 A* 28.8 ± 2.1 26.6 ± 1.1

{ }M-PGA5-2Di MT1 200 580 10 0.87 0.71 4.3 1.5 B 30.6 ± 4.4

M-PGA5-3 MT4 100 600 14 0.95 0.84 28.1 8.1 A* 26.4 ± 0.8M-PGA5-5 MT4 100 600 14 0.96 0.84 23.5 6.8 A* 28.7 ± 1.0M-PGA5-6 MT4 340 590 10 0.89 0.77 15.6 5.5 A 23.2 ± 1.0M-PGA5-7 MT4 400 520 5 0.41 0.64 2.8 1.6 A 27.0 ± 2.6

M-PGB2 10/2 M-PGB2-4 MT4 250 420 5 0.41 0.72 4.9 2.8 B* 9.2 ± 0.6 8.1 ± 1.2M-PGB2-5 MT2 475 575 5 0.55 0.70 4.2 2.4 A 6.8 ± 0.6

M-PGB3 7/2 M-PGB3-10 MT4 100 560 12 0.92 0.86 8.1 2.6 B* 7.1 ± 0.7 7.3 ± 0.1M-PGB3-9 MT4 100 590 13 0.92 0.87 11.1 3.4 A* 7.4 ± 0.5

M-PGB5 6/5 M-PGB5-1 MT4 100 540 11 0.73 0.88 14.3 4.8 A* 39.5 ± 1.8 40.4 ± 1.5M-PGB5-3 MT4 200 600 13 0.85 0.89 16.1 4.9 B* 40.1 ± 1.9M-PGB5-4 MT4 100 490 10 0.49 0.87 8.3 2.9 B* 40.0 ± 2.1M-PGB5-5 MT4 100 440 8 0.40 0.84 8.6 3.5 A* 38.5 ± 1.5

M-PGB5-7Di MT1 400 520 5 0.40 0.65 2.9 1.7 B 52.6 ± 4.8M-PGB7 4/2 M-PGB7-1 MT2 100 500 8 0.47 0.78 8.2 3.3 B 62.7 ± 2.8 63.0 ± 0.6

M-PGB7-2Ci MT1 20 430 6 0.39 0.72 2.1 1.0 B 64.1 ± 8.5

Notes: Determinations on standard inch samples are highlighted by a superscripted i added to the specimen name. n/N shows attempted versus successfulpalaeointensity determinations. Tmin and Tmax specify the temperature range of the straight line segment calculated over N p successive points. The fractionof the NRM (f ), the gap factor (g) and the quality factor (q) were calculated according to Coe et al. (1978). w denotes the weighting factor of Prevot et al.(1985). Class defines excellent (A) or good (B) quality according to the criteria. A superscripted star indicates alteration corrected analysis. H and Fw are thepalaeointensity values with associated standard deviation (SD) for the individual determination and the weighted site mean, respectively. The results enclosedby curely braces are from the same drill core and were averaged before calculating the site mean.

L-K9, there are less than four unsampled flows, and the directionschange from reversed (L-K6) to transitional state 1 (L-K7 and 8),and then back to a reversed direction (L-K9). Between flows L-K13 and L-K15 the direction changes from transitional state 1 tostate 2 within seven flows, equivalent to 5 m of the profile. Nopalaeosoil layers or erosional disconformities are found within ei-ther parts of the profile, which suggests high extrusion rates of thelavas.

Stable normal directions are absent in the sampled Lanai lavasand all transitional VGPs during the Gilsa excursion are restrictedto the southern hemisphere. Nevertheless, our Gilsa record could beincomplete due to the sporadic character of volcanic activity and thegaps between sampled units. ‘Normal’ directions during the Gilsawere particularly found in northern hemisphere records, DSDP site609B (Clement & Kent 1987), ODP site 983 and 984 (Channelet al. 2002), and the type location in Jokuldalur, Iceland (Watkins

C© 2009 The Authors, GJI, 179, 43–58



Figure 7. 40Ar/39Ar age spectra and isochron diagrams for three dated lava flows. Multiple subsamples from a flow are shown within a single diagram.

Table 3. 40Ar/39Ar data.

Site Sample Age spectrum Isochron analysisIncrements Probability 39Ar Age ± 2σ MSWD N 40Ar/36Ar ± 2σ Age ± 2σ MSWD(◦C) (per cent) (Ma) (Ma)

Lanai, KaumalapauL-K11 S59-74 0.35 58.90 1.646 ± 0.091 1.05 9 298.3 ± 5.0 1.55 ± 0.25 28.00

L-K15 S59-64 0.47 100.00 1.368 ± 0.076 0.93 7 291.0 ± 10.0 1.53 ± 0.38 41.00S59-65 0.25 100.00 1.427 ± 0.079 1.30 7 286.5 ± 9.3 1.74 ± 0.34 8.00S59-68 0.69 60.40 1.78 ± 0.10 0.56 5 299.8 ± 1.9 1.603 ± 0.082 1.04Weighted mean isochron age 1.60 ± 0.08

Maui, Pahihi GulchM-PGA7 S59-69 0.83 100.00 0.713 ± 0.027 0.46 7 296.7 ± 2.0 0.701 ± 0.029 3.90

Note: Summary of 40Ar/39Ar data of samples from Lanai and Maui.

et al. 1975; Udagawa et al. 1999). Clement & Kent (1987) alsofavour the interpretation of a geomagnetic field excursion becausethe normal directions do not stabilize in the 609B record. The veryshort duration, <8 kyr (Clement & Kent 1987; Channel et al. 2002)is one likely reason that a significant directional indication for theGilsa is not found in most sedimentary records. Another possibilitycould be that this event is more pronounced at high latitudes than

at low latitudes. An intensity minimum at approximately 1.62 Ma,however, is globally observed (Valet et al. 2005).

The onset of the Gilsa excursion as recorded in the North Atlanticsite 609B also shows an accumulation of VGPs southwest ofAustralia, similar to transitional field stage 2 from our Hawaiianrecord. This similarity, admittedly only based on two, at least sig-nificantly distant records, might suggest a dominance of dipolar

C© 2009 The Authors, GJI, 179, 43–58



-90 -45 0 45 900

2

4

6

Str

atig

rap

hic

leve

lInclination [°]

90 180 270

Declination [°]

0 10 20 30 40

Intensity [ T]

-90 -45 0 45 900

2

4

6

Str

atig

rap

hic

leve

l

Inclination [°]

90 180 270

Declination [°]

0 10 20 30 40

Intensity [ T]

-90 -45 0 45 900

1

2

3

4

5

Str

atig

rap

hic

leve

l

Inclination [°]

90 180 270

Declination [°]

0 10 20 30 40

Intensity [ T]

-90 -45 0 45 900

2

4

6

8

Str

atig

rap

hic

leve

l

Inclination [°]

90 180 270

Declination [°]

0 10 20 30 40

Intensity [ T]

L-K3-11

L-K12-15

L-K16-21

L-K22-28

Kaumalapali HarborKaumalapau Gulch

100

200

300

20

1

3

227,28

4

5

29

21

16

17-19

12

11

10

13-15

6-9

2223-26

2300

0123

09 77 7 1101

1 km

Lanai

Transitionalfield stage 1

Transitionalfield stage 2

1.55 ± 0.25 Ma

1.60 ± 0.08 Ma

Figure 8. Detailed map of sampling location at Kamalapau, Lanai, and palaeomagnetic results from four sections with successively exposed lavas. Transitionalfield states are emphasized by hatched areas. The dashed line in the palaeointensity diagram indicates the present-day field on Lanai (∼35 μT). Transitionalfield states 1 and 2 occur in the lowermost three sections.

components of the geomagnetic field during the onset of the excur-sion. When comparing our results of the Gilsa excursion to otherrecords of geomagnetic events during the Matuyama, surprisinglysimilar VGP movements in the beginning of these geomagneticevents are observed (Fig. 9). The onset of the Cobb Mountain po-larity subchron, also recorded in site 609B from the North Atlantic(Clement 1992), shows an initial VGP movement towards SouthAmerica followed by several flips towards south western Australia(Fig. 9b). Similar transitional field states at the beginning of thisevent, in particular transitional VGPs close to Australia, are foundin most palaeomagnetic Cobb Mountain records from the Atlanticand Pacific hemispheres and were also interpreted to give evidencefor a dipolar dominance (Clement 2000). The onset of the Punaru

cryptochron, which happened approximately 70 kyr prior to theCobb Mountain subchron (Singer et al. 1999) and was recorded ina volcanic sequence on Tahiti (Chauvin et al. 1990), includes southwest Australian VGPs associated by low field intensities (Fig. 9c).The 0.9-Myr-old Kamikatsura excursion recorded in Maui (Coeet al. 2004a) is characterized by transitional VGPs in South Americaand Australia (Fig. 9d). An approximately 0.795-Myr-old precur-sor to the Matuyama/Brunhes transition was recorded in volcanicrocks from Tahiti and Chile (Chauvin et al. 1990; Brown et al.1994, 2004; Singer et al. 2005). This precursor exhibits transitionalVGPs close to Australia (Fig. 9e). In summary, the recurrence ofsimilar VGP position in spatially distributed records of individualexcursions indicates a dominantly dipolar geomagnetic field at the

C© 2009 The Authors, GJI, 179, 43–58



a)

b)

c)

Lanai

1

2

3

4

5

<

<<<

609B

a

bc

d

e

f

g

hi

j

Tahiti

<<

6.2 T

29.9 T

7.7 T

6 T

19.5 T

14.0 T6.4 T

10.3 T

Cobb Mountain

Punaru

M/B precursor

Kamikatsurad)

e)

Tahiti

Tatara

Gilsa

Maui

Figure 9. Virtual geomagnetic poles (VGPs) for individual lavas (circles)and the five directional units (solid circles with 95 per cent-error ellipse)for Lanai (a). Also shown are the average palaeointensity values for thedirectional units. VGPs of the most detailed sedimentary Cobb Mountainrecord from DSDP site 609B (Clement 1992) are plotted in (b). Encircledletters emphasize the progression of VGPs in this record. In (c) the VGPsand average palaeointensities from the Punaru section on Tahiti (Chauvinet al. 1990) are shown. (d) depicts results from the Kamikatsura recordobtained on Maui, Hawaii (Coe et al. 2004a). The directional results of theMatuyama/Brunhes precursor recorded on Tahiti (Chauvin et al. 1990) andthe Tatara volcanic complex in Chile (Brown et al. 1994; Brown et al. 2004)are shown as solid circles and boxes, respectively, in (e). For the sake ofclarity only the onset of the recorded reverse to normal (R–N) transitionfrom the Punaru event, Tahiti and the Cobb Mountain record of 609B isshown.

onset of these events, the recurrence of similar transitional VGPpositions within the suggested preferred longitudinal bands (Lajet al. 1991) and close to the suggested VGP cluster regions(Hoffman 1992) in different excursions supports the hypothesisof an influence of lower mantle heterogeneities on the transitionalfield at least during the onset of these geomagnetic events. It shouldbe mentioned, however, that later transitional directions, related toR–N transitions, do not show this agreement with the preferred VGPpositions. In case of Figs 9(b) and (c) they tend to plot on centralPacific longitudes.

5.2 Maui

The isotopic age range of the volcanic Kula series from Maui (0.9–0.4 Ma, Naughton et al. 1980) indicates that the Matuyama/Brunhestransition is recorded within this series. A Brunhes age for the nor-mally magnetized lavas is supported by the 40Ar/39Ar age of 0.70 Mafor flow M-PGA7. The stratigraphically lower and therefore olderreversely magnetized flows were most likely formed during theMatuyama chron. A detailed record of the the Matuyama/Brunhesreverse to normal (R–N) transition, with several transitional direc-tions was previously also found in the post-shield Kula volcanicswithin the caldera of the Haleakala volcano at two different loca-tions (Baksi et al. 1992; Coe et al. 2004b) and was dated by the40Ar/39Ar method in both studies. The large distance between thePahihi Gulch and the eruption centre may account for the observa-tion that no transitional directions are present in our record.

The major aspect of the sampled Pahihi Gulch succession is therecording of the pre- and post-transitional behaviour of the ge-omagnetic field. Our results indicate low intensities prior to andan increasing strength of the geomagnetic field after the reversal.The obtained post-transitional palaeointensities after the reversalreach high intensity values, up to about twice of the present-day’sintensity of the Earth’s magnetic field at Maui (∼35 μT, Fig. 10).An almost identical observation of such intensity asymmetry acrossthe last reversal was found in a sedimentary record close to Hawaii(Theyer et al. 1985). A comparison of our absolute intensities withthose relative values of sedimentary record K78-10-30 emphasizesthe similarity (Fig. 10). Other globally distributed records from theMatuyama/Brunhes reversal, in particular the absolute palaeoin-tensity results from two profiles from La Palma, Canary Islands(Valet et al. 1999) also indicate weaker pre- and higher post-transitional field strength, although the asymmetry is not equallystrongly pronounced as in Hawaii. Yet, such feature does not onlyappear to be restricted to the last reversal. Herrero-Bervera & Valet(2005) found similar behaviour in the volcanic reversal records fromWaianae, Oahu. The volcanic record of a late Pliocene R–N transi-tion from Kauai, Hawaii also shows strong post-transitional fieldscompared to the pre-transitional state (Bogue 2001) and severalother detailed volcanic R–N transition records exhibit similar char-acteristics (e.g. Prevot et al. 1985; Leonhardt & Soffel 2002). Ageomagnetic field asymmetry across reversals appears to be at leasta characteristic of R–N transitional records. The unusually strongfield intensities after the reversal can be interpreted in terms of a sur-face geomagnetic field where the dipolar contribution is more dom-inant in the post-transitional field state than in the pre-transitionalstate. Such interpretation is supported by a geomagnetic field modelof the last transition, where non-dipolar contributions are signifi-cantly stronger prior to the reversal than afterwards (Leonhardt& Fabian 2007). A possible explanation for the underlying pro-cess of a field intensity asymmetry is suggested by comparisons to

C© 2009 The Authors, GJI, 179, 43–58



Figure 10. Intensity variation across the last reversal. The relative palaeoin-tensity variation and VGP latitude obtained in piston core K78-10-30 closeto Hawaii (Theyer et al. 1985) are shown in (a). The results from our profiles(b) show a similar asymmetry of palaeointensities across the reversal.

numerical geodynamo models. Such dynamo models point to twodifferent dynamic regimes within the Earth’s fluid outer core, withinand outside the tangent cylinder (Glatzmaier et al. 1999). The tan-gent cylinder is an imaginary cylinder, tangent to the equator of theEarth’s solid inner core. Simulated reversals of Glatzmaier et al.(1999) show that during most reversals poloidal and toroidal fieldschange their polarity first outside the tangent cylinder and then, afew thousand years later, within the cylinder. If the fields outsidethe tangent cylinder are getting more turbulent a significant timebefore the actual reversal, the surface geomagnetic field would stillbe dipolar dominated due to the reduced influence of short wave-length components of the field on the Earth’s surface. The surfacefield intensity, however, would be relatively low. After the fields re-versed within and outside the tangent cylinder, again a dominantlydipolar field is maintained. After the field reversed in both dynamicregimes, a fairly regular configuration of outer core magnetic fieldscould lead to a more strongly dipolar dominated state than prior tothe transition and, therefore, to comparably higher post-transitionalpalaeointensities in most locations on Earth.

6 C O N C LU S I O N

Lava flows sampled in a palaeomagnetic reconnaissance study onLanai, Hawaiian islands, recorded reverse and intermediate direc-tions of the geomagnetic field. 40Ar/39Ar age determinations show,that these lavas were formed approximately 1.6 Ma. This findingindicates, unlike previous age determinations on this island, that theearly evolution of Lanai is in agreement with the average age pro-gression of the Hawaiian hotspot. All intermediate palaeomagneticdirections fall in two specific groups, corresponding to VGPs west ofSouth America and southwest of Australia. The observation of inter-mediate directions suggest that the lava record represents the Gilsageomagnetic polarity excursion 1.6 Ma. Other globally distributed

records of the Gilsa excursion show similar VGP directions duringtheir onset, indicating a dipolar dominance during this time. Further-more, similar transitional field states, in particular transitional VGPsclose to Australia are found in most palaeomagnetic records fromgeomagnetic excursions during the Matuyama chron. The locationsof the transitional field stages correspond to suggested preferred po-sition of VGPs, which were related to zones of low seismic velocitiesin the lower mantle (Laj et al. 1991; Hoffman 1992). Therefore, ourresults support the hypothesis of an influence of lower mantle het-erogeneities on the geomagnetic field at least during the onset ofthe polarity events. Absolute palaeointensity determinations usingmodifications of the Thellier technique point to generally low fieldintensities on Hawaii during this time, which decrease to values of4.6 μT during transitional states. Palaeointensities, however, couldbe obtained only from 6 of 30 sampled lavas on Lanai. The presenceof post-genetic titanomaghemites in these rocks, as well as signif-icant alteration during thermal laboratory treatment affecting thecoercivity spectrum and, therefore, very likely the average domainstate of the samples lead to this very low success rate. The palaeoin-tensity determination success rate is somewhat higher for the lessaltered lavas sampled on Maui, which contain a record of the lastgeomagnetic reversal, the Matuyama/Brunhes reversal. Palaeoin-tensity increases from very low pre-transitional field strengths of8–63 μT, about twice the present-day field after the reversal. Transi-tional directions were not found in the sampled sequence. A similarstrong difference of pre- and post-transitional fields is also foundin a sedimentary piston core record close to Hawaii, supportingour conclusion that the geomagnetic field asymmetry during theMatuyama/Brunhes reversal was particularly pronounced close toHawaii.

A C K N OW L E D G M E N T S

We would like to thank the Haleakala Ranch for sampling permis-sion. Emilio Herrero-Bervera and Rob Coe are acknowledged fortheir support during preparation of the field work. Brad Clementkindly provided the data set of site 609B. Constructive reviewsby Carlo Laj, Jean-Pierre Valet and Emilio Herrero-Bervera signifi-cantly improved the manuscript. We profited from many discussionswith David Krasa and Christoph Heunemann. Sampling was fundedby the German Science Foundation (He1814/9-1).

R E F E R E N C E S

Baksi, A.K., Hsu, V., McWilliams, M.O. & Farrar, E., 1992. 40Ar/39Ardating of the Brunhes-Matuyama geomagnetic field reversal, Science,256, 356–357.

Bogue, S.W., 2001. Geomagnetic field behavior before and after the Kauaireverse-normal polarity transition, J. geophys. Res., 106, 447–461.

Bogue, S.W. & Coe, R.S., 1984. Transitional paleointensities from Kauai,Hawaii, and geomagnetic reversal models, J. geophys. Res., 89, 10 341–10 354.

Bonhommet, N., Beeson, M.H. & Dalrymple, G.B., 1977. A contributionto the geochronology and petrology of theisland of Lanai, Hawaii, Geol.soc. Am. Bull., 88, 1282–1286.

Brown, L.L., Pickens, J.C. & Singer, B., 1994. Matuyama-Brunhes transitionrecorded in lava flows of the Chilean Andes: evidence for dipolar fieldduring reversals, Geology, 22, 299–302.

Brown, L.L., Singer, B.S., Pickens, J.T. & Jicha, B.R., 2004. Paleomagneticdirections and 40Ar/39Ar ages from the Tatara-San Pedro volcanic com-plex, Chilean Andes: lava record of a Matuyama-Brunhes precursor? J.geophys. Res., 109, B12101, doi:10.1029/2004JB003007.

C© 2009 The Authors, GJI, 179, 43–58



Butler, R.F., 1992. Paleomagnetism: Magnetic Domains to Geologic Ter-ranes, Blackwell Scientific Publications, Oxford.

Channel, J.E.T., Mazaud, A., Sullivan, P., Turner, S. & Raymo, M.E., 2002.Geomagnetic excursions and paleointensities in the Matuyama chron atOcean Drilling Program sites 983 and 984 (Iceland basin), J. geophys.Res., 107, EPM 1-1–1-14.

Chauvin, A., Roperch, P. & Duncan, R.A., 1990. Records of geomagneticreversals from volcanic islands of French Polynesia 2. Paleomagneticstudy of a flow sequence (1.2-0.6 Ma) from the island of Tahiti anddiscussion of reversal models, J. geophys. Res., 95, B, 2727–2752.

Clague, D.A. & Dalrymple, G.B., 1987. The Hawaiian-Emperor volcanicchain, Part I: geological evolution, in Volcanism in Hawaii, pp. 5–54,eds Decker, R.W., Wright, T.L. & Stauffer, P.H., U.S. Geological Survey,Denver.

Clement, B.M., 1992. Evidence for dipolar fields during the Cobb Mountaingeomagnetic polarity reversal, Nature, 358, 405–407.

Clement, B.M., 2000. Comment on the Lau Basin Cobb Mountainrecords by Abrahamsen and Sager, Phys. Earth planet. Inter., 119,173–184.

Clement, B.M. & Kent, D.V., 1987. Short polarity intervals within theMatuyama: transitional field records from hydraulic piston cored sedi-ments from the North Atlantic, Earth planet. Sci. Lett., 81, 253–264.

Coe, R.S., 1974. The effect of magnetic interactions on paleointensity deter-minations by the Thelliers’ method, J. Geomagn. Geoelectr., 26, 311–317.

Coe, R.S., Gromme, S. & Mankinen, E.A., 1978. Geomagnetic paleointen-sities from radiocarbon-dated lava flows on Hawaii and the question ofthe Pacific nondipol low, J. geophys. Res., 83, 1740–1756.

Coe, R.S., Gromme, S. & Mankinen, E.A., 1984. Geomagnetic paleointeni-ties from excursion sequences in lavas on Oahu, Hawaii, J. geophys. Res.,89(B2), 1059–1069.

Coe, R.S., Riisager, J., Plenier, G., Leonhardt, R. & Krasa, D., 2004a. Mul-tidomain behaviour during Thellier paleointensity experiments: resultsfrom the 1915 Mt. Lassen flow, Phys. Earth planet. Inter., 147, 141–153.

Coe, R.S., Singer, B.S., Pringle, M.S. & Zhao, X., 2004b. Matuyama-Brunhes reversal and Kamikatsura event on Maui: paleomagnetic di-rections, 40Ar/39Ar ages and implications, Earth planet. Sci. Lett., 222,667–684.

Day, R., Fuller, M.D. & Schmidt, V.A., 1977. Hysteresis properties of titano-magnetites: grain size and composition dependence, Phys. Earth planet.Inter., 13, 260–266.

Doell, R.R., 1972a. Paleomagnetism of lava flows from Kauai, Hawaii, J.geophys. Res., 77, 862–876.

Doell, R.R., 1972b. Paleosecular variation of the Honolulu volcanic series,Oahu, Hawaii, J. geophys. Res., 77, 2129–2138.

Doell, R.R. & Cox, A., 1961. Palaeomagnetism of Hawaiian lava flows,Nature, 192, 645–647.

Doell, R.R. & Cox, A., 1965. Paleomagnetism of Hawaiian lava flows, J.geophys. Res., 70, 3377–3405.

Duffield, W.A. & Dalrymple, G.B., 1990. The Taylor Creek Rhyolite of NewMexico: a rapidly emplaced field of lava domes and flows, Bull. Volcanol.,52, 475–487.

Fisher, R.A., 1953. Dispersion on a sphere, Proc. R. Soc. Lond. A, 217,295–305.

Glatzmaier, G.A., Coe, R.S., Hongre, L. & Roberts, P.H., 1999. The role ofthe Earth’s mantle in controlling the frequency of geomagnetic reversals,Nature, 401, 6756, 885–890.

Hacker, B.R., Modenfelder, J.L. & Gnos, E., 1996. Rapid emplacement ofthe Oman ophiolite: thermal and geochronologic constraints, Tectonics,15, 1230–1247.

Heller, F. & Petersen, N., 1982. Self-reversal explanation for theLaschamp/Olby geomagnetic field excursion, Phys. Earth planet. Inter.,30, 358–372.

Herrero-Bervera, E. & Coe, R.S., 1999. Transitional field behavior during theGilbert-Gauss and Lower Mammoth reversals recorded in lavas from theWai’anae volcano, O’ahu, Hawaii, J. geophys. Res., 104, 29 157–29 173.

Herrero-Bervera, E. & Valet, J.-P., 1999. Paleosecular variation during se-quential geomagneticreversals from Hawaii, Earth planet. Sci. Lett., 171,139–148.

Herrero-Bervera, E. & Valet, J.-P., 2005. Absolute paleointensity and rever-sal records from Waianae sequence (Oahu, Hawaii, USA), Earth planet.Sci. Lett., 234, 279–296.

Herrero-Bervera, E., Margas-Vinuela, J. & Valet, J.-P., 2000. Paleomag-netic study of the ages of lavas on the island of Lanai’i, Hawaii, J. Volc.Geotherm. Res., 104, 21–31.

Hoffman, K.A., 1992. Dipolar reversal states of the geomagnetic field andcore mantle dynamics, Nature, 359, 789–794.

Hoffman, K.A., 1996. Transitional paleomagnetic field behavior: preferredpaths or patches? Surv. Geophys., 17, 207–211.

Krasa, D., 2003. Self-Reversal of Remanent Magnetisation of Basalts—Origin, Mechanisms and Consequences, PhD thesis, Ludwig-Maximilians-Universitat, Munchen.

Krasa, D., Heunemann, C., Leonhardt, R. & Petersen, N., 2003. Experimen-tal procedure to detect multidomain remanence during Thellier-Thellierexperiments, Phys. Chem. Earth, 28, 681–687.

Laj, C. & Kissel, C., 1999. Geomagnetic field intensity at Hawaii for thelast 420 kyr from the Hawaii Scientific Drilling Project core, Big Island,Hawaii, J. geophys. Res., 104, 15 317–15 338.

Laj, C., Mazaud, A., Weeks, R., Fuller, M. & Herrero-Bevera, E., 1991.Geomagnetic reversal paths, Nature, 351, 447.

Laj, C., Szeremeta, N., Kissel, C. & Guillou, H., 2000. Geomagnetic pale-ointensities at Hawaii between 3.9 and 2.1 Ma: preliminary results, Earthplanet. Sci. Lett., 179, 191–204.

Laj, C., Kissel, C., Scao, V., Beer, J., Thomas, D.M., Guillou, H., Muscheler,R. & Wagner, G., 2002. Geomagnetic intensity and inclination variationsat Hawaii for the past 98 kyr from core SOH-4: a new study and acomparison with existing contemporary data, Phys. Earth planet. Inter.,129, 205–243.

Langenheim, V.A.M. & Clague, D.A., 1987. The Hawaiian-Emperor vol-canic chain, Part II: stratigraphicframework of volcanic rocks of theHawaiian Islands, in Volcanism in Hawaii, pp. 55–84, eds Decker, R.W.,Wright, T.L. & Stauffer, P.H., U.S. Geological Survey, Denver.

Leonhardt, R. & Fabian, K., 2007. Paleomagnetic reconstruction of theglobal geomagnetic field evolution during the Matuyama/Brunhes tran-sition: iterative Bayesian inversion and independent verification, Earthplanet. Sci. Lett., 253, 172–195.

Leonhardt, R. & Soffel, H.C., 2002. A reversal of the Earth’s magnetic fieldrecorded in midMiocene lava flows of Gran Canaria: paleointensities J.geophys. Res., 107(B11), 2299, doi:10.1029/2001JB000949.

Leonhardt, R., Hufenbecher, F. & Heider, F. and Soffel, H., 2000. Highabsolute paleointensity during a mid Miocene excursionof the Earth’smagnetic field, Earth planet. Sci. Lett., 184, 141–154.

Leonhardt, R., Matzka, J. & Menor, E.A., 2003. Absolute paleointensi-ties and paleodirections from Fernando de Noronha, Brazil, Phys. Earthplanet. Inter., 139, 285–303.

Leonhardt, R., Heunemann, C. & Krasa, D., 2004a. Analyzing ab-solute paleointensity determinations: acceptance criteria and thesoftware ThellierTool4.0, Geochem. Geophys. Geosys., 5, Q12016,doi:10.1029/2004GC000807.

Leonhardt, R., Krasa, D. & Coe, R.S., 2004b. Multidomain behavior duringThellier paleointensity experiments: a phenomenological model, Phys.Earth planet. Inter., 147, 127–140.

Mankinen, E.A. & Champion, D.E., 1993. Latest Pleistocene andHolocene geomagnetic paleointensity on Hawaii, Science, 262,412–416.

McDougall, I. & Wensink, H., 1966. Paleomagnetism and geochronol-ogy of the Plio-Pleistocene lavas in Iceland, Earth planet. Sci. Lett., 1,232–236.

McFadden, P.L. & McElhinny, M.W., 1988. The combined analysis of re-magnetization circles and direct observations in palaeomagnetism, Earthplanet. Sci. Lett., 87, 161–172.

Naughton, J.J., Macdonald, G.A. & Greenberg, V.A., 1980. Some additionalPotassium-Argon ages of Hawaiian rocks: the Maui volcanic complexof Molokai, Maui, Lanai and Kahoolawe, J. Volc. Geotherm. Res., 7,339–355.

Prevot, M., Mankinen, E.A., Coe, R.S. & Gromme, S., 1985. The SteensMountain (Oregon) geomagnetic polarity transition 2. Field intensity

C© 2009 The Authors, GJI, 179, 43–58



variations and discussion of reversal models, J. geophys. Res., 90, 10 417–10 448.

Riisager, P. & Riisager, J., 2001. Detecting multidomain magnetic grainsin Thellier paleointensity experiments, Phys. Earth planet. Inter., 125,111–117.

Singer, B.S., Hoffman, K.A., Chauvin, A., Coe, R.S. & Pringle, M.S., 1999.Dating transitionally magnetized lavas of the late Matuyama chron: to-wards a new 40Ar/39Ar timescale of reversals and events, J. geophys. Res.,104, 679–693.

Singer, B.S., Hoffman, K.A., Coe, R.S., Brown, L.L., Jicha, B.R., Pringle,M.S. & Chauvin, A., 2005. Structural and temporal requirements forgeomagnetic field reversal deduced from lava flows, Nature, 434, 633–636.

Stearns, H.T. & Macdonald, G.A., 1942. Geology and groundwater resourcesof the Island of Maui, Hawaii, Hawaii Div. Hydrogr. Bull., 7, 344 pp.

Steiger, R.H. & Jager, E., 1977. Subcommision on geochronology: conven-tion on the use of decay constants in geo- and cosmochronology, Earthplanet. Sci. Lett., 36, 359–362.

Teanby, N., Laj, C., Gubbins, D. & Pringle, M., 2002. A detailed palaeoin-tensity and inclination record from drill core SOH1 on Hawaii, Phys.Earth planet. Inter., 131, 101–140.

Theyer, F., Herrero-Bervera, E. & Hsu, V., 1985. The zonal harmonic modelof polarity transitions: a test using successive reversals, J. geophys. Res.,90, 1963–1982.

Udagawa, S., Kitagawa, H., Gudmundsson, A., Hiroi, O., Koyaguchi, T.,Tanaka, H., Kristjansson, L. & Kono, M., 1999. Age and magnetism oflavas in Jokuldalur area, Eastern Iceland: Gilsa event revisited, Phys.Earth planet. Inter., 115, 147–171.

Valet, J.-P., Brassart, J., Le Meur, I., Soler, V., Quidelleur, X., Tric, E. &Gillot, P.-Y., 1996. Absolute paleointensity and magnetomineralogicalchanges, J. geophys. Res., 101(B11), 25 029–25 044.

Valet, J.-P., Brassat, J., Quidelleur, X., Soler, V., Gillot, P.-Y. & Hongre, L.,1999. Paleointensity variations across the last geomagneticreversal at LaPalma, Canary Islands, Spain, J. geophys. Res., 104, 7577–7598.

Valet, J.-P., Meynadier, L. & Guyodo, Y., 2005. Geomagnetic dipolestrength and reversal rate over the past two million years, Nature, 435,802–805.

Watkins, N.D., Kristjansson, L. & McDougall, I., 1975. A detailed paleo-magnetic survey of the type location for the Gilsa geomagnetic polarityevent, Earth planet. Sci. Lett., 27, 436–444.

Wensink, H., 1964. Secular variation of the Earth magnetism in Plio-Pleistocene basalts of eastern Iceland, Geol. Mijnb., 43, 403–413.

West, H.B., Garcia, M.O., Gerlach, D.C. & Romano, J., 1992. Geochem-istry of tholeiites from Lanai, Hawaii, Contr. Mineral. Petrol., 112,520–542.

Yamamoto, Y., Tsunakawa, H. & Shibuya, H., 2003. Palaeointensity study ofthe Hawaiian 1960 lava: implications for possible causes of erroneouslyhigh intensities, Geophys. J. Int., 153, 263–276.

C© 2009 The Authors, GJI, 179, 43–58


Documents

The Gilsá excursion and the Matuyama/Brunhes transition recorded in 40Ar/39Ar dated lavas from Lanai and Maui, Hawaiian Islands