Petrology and. K-Ar ages of dredged samples’from Laysan Island and Northampton Bank volcanoes, Hawaiian Ridge, and evolution of the Hawaiian-Emperor chain
G. PI. DALRYMPLE D. A. CLAGUE 1 US.Geological Sihey. 345 Middlefield Road, Menlo Park, California 94025 M. 0. GARCIA Hawaii Institute of Geophysics, Univehity of Hawaii at Manoa, 2525 Correa Road, Honolulu, Hawaii 96822 S. W. BRIGHT Department of Geology, Middlebury College. Middlebury, Vermont 05753
Geological Society of America Bulletin, Part II, v. 92, p. 884-933, Figs. 9, Tables 8, June, 1981, Doc. no. M10601
Hawaiian-Emperor chain was formed as INTRODUCTION the Pacific lithospheric plate moved
The Hawaiian-Emperor volcanic chain first northward and then northwestward
is made up of at least 107 indentifiable relative to the Hawaiian hot spot,
shield volcanoes (Chase and others, a more or less stable melting anomaly
1970; Bargar and Jackson, 1974; Clague in thc asthenosphere, and that the
and others, 1980) and is the longest bend in the,chain reflects a majur linear island and seamount chain in change in Paci,fic plate motion.
the Pacific (Fig. 1). Beginning at Several mechanisms have been proposed
the active volcanoes Kilauea and Mauna to explain the Hawaiien (and other)
Loa on the island of Hawaii, this chain hot spots, including a propagating
of volcanoes extends west-northwestward fracture (Betz and Hess, 1942;
along the Hawaiian Ridge fo> a distance Jackson and Wright, 1970) ; diapiric
of 3,500 km, where it turns northward upwelling along a line of structural
and continues another 2,300 km as the weakness (Green, 1971; McDougall,
Emperor Seamounts, ending near the 1971) ; thermal (Morgan, 1972a, 1972b)
intersection of the Aleutian and Kurile or chemical (Anderson, 1975) plumes
Trenches. of gravitationally unstable material
It is now thought that the rising from the deep mantle; shear 884
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160' '1800 160. 140' 120.
yb 2%
- PAC'IFIC OCEAN tg3 Zd
I I
lnnamod Smls
30' I LAYSAN ISLAND I
NORTHA~P~OF; *? BANK Plnnocle
- 200
I I .170° 1800 170' 160. l!
Figure 1. Bathymetric map of the Hawaiian Ridge showing the locations of Laysan Isl,and and"Northampton Bank. Other radiometrically dated volcanoes are identified by name. -Contour interval is 1 km and based on bathymetry by Chase and others (1970). Inset shows the location of the Hawaiian-Emperor volcanic chain in the North Pacific.
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melting coupled with thermal feedback should have evolved chemically in some
(Shaw, 1973) and geographically systematic way if the volcanoes were
stabilized by gravitational sinking fed from a single melting anomaly.
of refractory residua (Shaw and Jackson, These corollaries have been the
1973); and'extrusior) induced by lateral subject of considerable research on
motion along plate boundaries the Hawaiian-Emperor chain over the
(Handschumacher, 1973). Despite past decade or so, culminating in Deep
the variety of dynamic models proposed, Sea Drilling Project (DSDP) Leg 55
there has yet to be devised a drilling in the Emperor Seamounts,
definitive experiment to test any during whiCh volcanic rocks wcre
of them. All these mechanisms are, cored on three of the volcanoes
however, encompas'sed by the general (Jackson, Koizumi, and others, 1980).
(or kinematic) hot spot hypothesis, The validity of these two corollaries"
which, when used in the broadest has been verified by extensive K-Ar
sense, implies neither mechanism radiometric and petrologic studies
nor excess .heat. in both the islands and the dominantly
The general hot spot hypothesis submarine sections of the chain. In
has two important kinematic the most recent K-Ar study and
cdrollaries that are independent synthesis, Dalrymple and others (1980b)
of hot-spot fixity and can b'e tested showed that the ages of 27 dated volcanoes
directly, using age and petrologic increase systematically at a rate of
data. One is that the ages of the about 0.0125 m.y./km (8 cm/yr) from the
volcanoes in a linear chain should active volcanoes Kllauea and Nauna
increase as a function of distance Loa (0 m.y.1 to Suiko Seamount
from the hot spot. The second is (64.7 ? 1.1 m.y.), more than 1,300 km
that the lavas of the volcanoes north of the Hawaiian-Emperor bend
should be chemically similar or (Fig. 1). Petrologic and chemical
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studies have shown that the volcanoes of volcanic propagation in the
of the chain closely resemble Hawaiian Hawaiian-Edperor chain, Dalrymple and
volcanoes in both the major- and trace- others (1980b) noted that there were
element chemistry of the lavas and in three major sections of the chain fnr
the sequence and volumes in which the which age data did not yet exist.
principal rock suites occur (Kirkpatrick The gap between Suiko and Meiji Seamounts
and others, 1980; Jackson and others, (Fig. 1) will be difficult to fill
1980). In addition to the age and without drilling because the seamounts
chemical data, the Leg 55 results showed north of Nintoku are covered by a blanket
that Suiko Seamount formed at a latitude of ice-rafted debris. The gap immediately
of 26.9' t 3.5', that the Hawaiian hot east of the bend will never be
spot has been at relatively low latitudes completely filled because there are
for the past 65 m.y. (Kono, 1980), and only two' volcanoes in this section of
that the Emperor volcanoes were'once the chain. The third gap is a
islands that have since spbsided 2,000'm 1,070-km-long section between La Perouse
or more beneath the &a (see summary in Pinnacle and Pearl and Hermes Reef.
Jackson and otbers, 1980). Thus, not The purpose of this paper is to report ,...~ _* only is the (approximately) fixed hot spot new K-Ar and chemi'cal data on samples
hypothesis a reasonable explanation for from Laysan Island and Northampton Bank
the origin of the entire Hawaiian-Emperor 'volcanoes, which lie near the center of
volcanic chain, but also the Emperor the La Persouse-Pearl and Hermes gap.
volcanoes apparently have construgtional, SAMPLE LOCATIONS AND DESCRIPTIONS erosional, and subsidence histories very
similar to those of the well-studied Northampton Bank is
Hawaiian Islands (Steams, 1966; Macdonald Q600 km southeast of Midway Islands.
and Abbott, 1970). The volcano rises to within 33 m of
In their synthesis of the chronology mean sea level, is roughly conical,
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33 and has a volye of 6.8 x 10 km (Bargar is nearly twice as large as Northampton
and Jackson, 1974), about the same size Ba.ik and comparable in, size to Lanai.
as West Maui. Samples were recovered It is slight6 elongate east-west and
by the University of Hawaii R/V Kana is topped by a large, flat platform
Keoki in one dredge in 1,160 m of water from which rises a small coral island.
on the south side of the volcano at lat. The samples studied were
2.5O 17.8'N, long. 172' 01.3'W. The recovcred in a single dredge during
dredge recovered approxirgately equal cruise LEE8-76-NP (Dalrymplc and
volumes of volcanic rock and biogenic others, 1980a) on the north side'of the
carbonate weighing 2 total of 168 kg. volcano at lat. 25' 54.8'N, long.
The volcanic rock samples recovered 171' 46.3'W from a water depth of 690
from Northampton Bank are angular and to 350 m. The dredge recovered 16
massive, and they range from 7 to 35 cm volcanic rocks and 8 small fragments
in length. Most samples have no manganese of coralline material. The volcanic
coating, although some have manganese rocks are well rounded and range from
crusts as thick as 1-2 mm. Larger samples 3 to 28 cm in length; most are massive
have a 1- to 2-cm-thick weathered rim with a platy cleavage. All samples
characterized by altered olivine. The have manganese coating that range in
interior of most samples-& fresh, with thickness from patina to about 0.5 mm.
little or no olivine alteration. All of Two of the samples are conglomerates
the volcanic rocks appear identical in of volcanic cobbles and pebbles in a
hand sample and could be from a single matrix of carbonate silt. Most samples
flow or dike. are weathered to brown near the outer
Laysan Island is adjacent to and about surface, but are Cresh inside the
60 km northeast of Northampton Bank 0- to 0.5-cm-thick alteration rind; 33 (Fig. 1). With a volume of 11.3 x 10 km some of the smaller pebbles are
(Bargar and Jackson, 1974), Laysan volcano weathered throughout.
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greater within one sample than between PETROGRAPHY, MINERALOGY, AND GEOCHEMISTRY ' the averages of the three samples
Petrographically, the samples from analyzed. Compositions of groundmass
Northampton Bank are similar, except in plagioclase grains in the three
the content of oliwine phenocrysts, Northampton Bank samples fall within
which ranges from 5% to 25% by volume. the range of compositions of plagioclase
All of the samples are nearly in tholeiitic volcanic rocks from
holocrystalline (<5% glass), and all Maui, although the Northampton Bank
contain-olivine as the sole phenocryst samples contain somewhat more K 0 2 phase. The groundmass consists of (O.W+ 0.01 versus 0.23 2 0.02 wt %
very pale brown augite (-40%), plagioclase K20; Keil and others, 1972). Clino-
(-30%), iron-titanium oxides (20%-25%), pyroxene compositions of 'the Northampton
glass (-5%), and olivine ( three dated samples are fairly fresh Hawaiian tholeiitic clinopyroxene and contain unaltered olivine cr.ystals, (Fodor and others, 1975) but'are some- although nearly all of the olivine'is what enriched in Ti02. At present, partly replaced along fractures by a olivine in tholeiitic basalt cannot fibrous greenish-brown smectite. be distinguished from that in alkalic The individual analyzed and dated basalt (Fodor and others, 1977). samples are described in detai3- in Phenocrysts of olivine in the Northamp-Dn the Appendix. Bank basalt are essentially homogeneous, Chemical analyses of olivine pheno- although.some grains have optical crysts and of groundmass plagioclase discontinuities near their margins. The -.and clinopyroxene grains were made by forsterite content of sample 5-4c is electron microprobe (Table 1). greater than any value reported by Variations in mineral compositions Fodor and others (1977) for volcanic rocks from Maui (Fogg versus Fo are small and, except for olivine, 85) ' Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 890 TABLE 1. MICROPROBE MINERAL COMPOSITIONS OF BASALT SAMPLES DREDGED FROM NORTHAMPTON BA~KSEAMOUNT, HAWAIIAN CHAIN. Ti02 1.54 1.48 1.85 ~1~0~4.38 3.97 3.66 29.6‘0 28.38 29.24 Cr 0 0.45 0.25 0.19 23 FeO 7.82 8.28 8..52 0.86 0.84 0.84 16.13 16.27 16.14 10.71 MnO 0.21 0.18 0.19 0.23 0.22 0.18 0.16 0.. . MgO 16.01 15.31 14.96 43.05 13.07 ,43.07 47.43 CaO 19.19 20.05 ,20.38 14.32 13.38 13.30 0.35 0.34 0.35 0.25 Na20 0.25 0.25 0.24 3.76 4.17 4.05 0.12 0.14 K2° 0.13 0.38 0.39 0.37 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 The results of whole-rock analyses of suggest that the Northsmpton Bank tholeiite the three Northampton Bank samples was generated from a mantle source broadly (Table 2) are very similar. The samples similar to that which generated the basalt are clearly of tholeiitic basalt similar making up the shields of the Hawaiian to the shield-building tholeiitic basalt Islands. that forms the bulk or the exposed The samples from Laysan Island Hawaiian Islands. Compositionally, the 'petrographically are similar to one ancther; Northampton Bank tholeiite most closely all are hawaiite and mugearite with textures resembles Kilauea tholeiite (Wright, 1971: ranging from intergranular to subtrachytic. although the Northampton Bank samples On the basis of the dominant groundmass * contain less A1 230 than do Kilauea ferromagnesian mineral, and samples fall samples with the same MgO content. into two main groups. About one-half of the Trace-element data for two of the samples contain abundant groundmass clino- Northampton Bank samples (Table 2) confim pyroxene and little to no groundmass; the the oceanic-island tholeiitic composition other half contain less clinopyroxene and of the basalt. These samples clearly more olivine (see Appendix). Most of the contain more Sr, Ba, and Rb than rocks are moderately altered and contian mid-ocean-ridge basalt and closely from 2% to 23% smectite, mostly replacing resemble tholeiitic basalt of the exposed glass. All of the olivine is replaced by Hawaiian shields (Leeman and others, 1980; "iddingsite." No secondary calcite was D. A. Clague, unpub. data). The K/Ba was observed. All but two of the samples ratios in these samples average 31, are massive (<2.5% vesicles). Most samples identical to those in tholeiitic basalt contain sparse phenocrysts and micro- from the Hawaiian Islands and in other phenocrysts of plagioclase and opaque dredged samples of tholeiitic basalt from Fe-Ti oxides f olvine. Four. samples along the chain (Clague and Frey, 1979; contain a few grains of reddish Leeman and others, 1980). These results biotite in the groundmass. Apatite Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 892 TAELE 2. WHOLE-ROCK CHEMICAL ANALYSES AND TRACE-ELEMENT DATA OF NORTHAMPTON BANK DREDGE SAMPLES. Na20 2.09 2.06 2.05 0.40 0.32 0.28 K2° 1.83 2.51 1.87 H2° Ti02 2.32 2.28 2.36 0.23 0.24 0.23 '2'5 MnO 0.16 0.16 0.17 0.11 0.12 0.04 c02 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 893 is present as tiny needles in nearly magmas, but, if so, the fractionated every sample. bulk mineral assemblage must have been The major-element analyses oV14 sample different 'for each group. The physical from Laysan Island volcano (Table 3) conditions under which the parent magma closely resemble those of Hawaiian crystallized and fractionated could be hawaiite and mugearite from the alkalic responsible for the two fractionation eruptive stage (Macdonald, 1968). None trends, although it is equally feasible of these lavas represents unmodified that the two groups had compositionally mantle melts because they are not in distinct parental magmas. These two equilibrium with olivine of mantle groups correspond to the two groups composition. All of the Laysan Island identified petrograpbically and described samples ar6 of differentiated lavas above. derived by crystal fractionation from Trace-element data (Table 3) confirm a more magnesian alkali basalt parental the alkalic nature of the Laysan lavas. magma or magmas. Most of the focks Compared to tholeiitic basalt, these are suffi'ciently altered that quanti- lavas are strongly enriched in the tative evaluation of the shallow crystal incompatible elements K 0, Sr, 2 P205, fract'ionation that led to their formation and Ba. The low Ni, Cr, and Co (sample is difficult. Two discrete fractionation D1-2) contents indicate that the lavas trends, however, are evident on a plot underwent fairly extensive olivine of A1 0 versus CaO (Fig. showing (cwrtXdng a trac-e of Cr-spinel) 23 2), that samples containing less than 8 wt % fractionation before eruption. Likewise, CaO and those containing more than 8 wt the low Sc content indicates fractionation % CaO cannot be related by continuous of clinopyroxeie, and the nearly constant crystal fractionation. Both groups of Sr content suggests that plagioclase diffekentiated lavas possibly could be was a significant component of the derived from.the same or similar parent fractionated mineral assemblage. The Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 8981 TABLE 3. WHOLE-ROCK CHEMICAL ANALYSES AND TRACE ELEMENT DATA FOR SAMPLES DREDGED FROM LAYSAN ISLAND. sc 17 17 20 13 10 13 13 V 280 330(329) 137 104 101 186 90 Cr 48 67(32) 49 53 50 37 51 ni 31 20(22) 28 14 19 21 17 Zn 162 127 ( 1 1 1 139 126 '153 164 136 Rb 21 2j(27) 20 ' 40 63 39 54 Sr 980 820(831) 800 1250 940 1100 1100 Zr 240 235(240) 325 315 380 315 360 Ba 445 405(509) 600 590 700 550 720 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 895 TABLE 3. (SONTINUED) Si02 43.92 46.22 47.96 50.38 47.02 46.09 ,114. go 17.10 15.46 *l2'3 15.31 17.5j 17.16 17.27 15.70 FeO* 11 -95 12.80 11.47 8.47 12 * 92 10.82 11.12 Mgo 5.39 2.90 2.49 2.97 2.27 4.12 4.56 15 CaO 9.37 6.24 5.79 6.13 5.76 8.97 9!16 / Na20 2.98 3.99 4.57 4.37 4 .4 9 3.44 -\ 4.34 2.19 2.41 2.61 2e.10 1.64 1.67 K2° 1.53 Ti02 4.27 3.07 2.58 2.11 3.03 3.86 - 3.61 1.03 '2'5 .78 .77 .87 .70 .74 .74 MnO .14 .20 .17 -13.. .12 .16 - 19 _-_------Total 95.64 95.48 95.84 95.03 96.01 95.54 95.75 sc 14 15 10 7 19' 16 14 V 285 131 97 61 138 235 240 cr 51 59 49 42 ,' 48 34 47 ni 27 20 18 20 9 19 13 zrl 150 144 152 135 139 140 103 Rb 34 52 52 70 55 38 41 Sr 1000 920 1000 1000 900 960 920 Zr 255 350 375 425 315 280 280 Ba 455 560 560 740 570 .440 500 Note: Oxide .analyses in weight percent, trdce element analyses Si02, K P205, in ppm. A120 , FeO', CaO, 20, Ti02, and MnO by X-ray fluorescenze (XRF); analysts, S. Brigh , and D. A. Clague. MgO, Na20, and all trace elements by XRF; analyst J. Carr, project leader V. G. Mossotti, U.S. Geologica_k Survey. Sample Dl-2 was also analyzed for trace elements at Woods Hole Oceanographic Institution by R. Brackett. The data are shown in parentheses. In addition to the element contents listed, this sample has Nb = 55 ppm, Y = 33 ppm, Cu = 19 ppm, and Co = 36 ppm. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 '89 G .. __ -- - I LAYSAE; 1 -1 : fractfractionation onat on trends I m I 0 17- N 4 4 I 15I I; I I 5 6 7 8 9 18 '1 1 Figurc 2. Plo; of A1,O. versus CaO for the Laysan lslana hawaiitcs bnd L .2 mugearitcs. lhe two discrcte fractionation trends cmnot be related by continuous crystal fractionation.of any reasonable mineral assemblage. The iwo fractionafion siquances may bc derived from a single parent alkali basalt magma under dif f crcnt physical conaitions or from discretc parent magma. Datz plottca zrc dry reducc&r.ormalized. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 897 decrease in V with lncreasing Zr and lavas (28) is similar to that of slkalic decreasing MgO reflects the crystalli- basalt of the alkalic eruptive stage zation and fractionation of titanomag- from East Molokai (Clague and Beeson, netite. This conclusion is consistent 1980) and Hualalai (Clague and others, with the presence of abundant micropheno- 1981), but differs from that (15) of crysts of titanomagnetite in many of Hawaiian post-erosional alkalic lavas these lavas. The most differentiated (Clague and Frey, 1979). These data lavas, those with the highest Zr and the all indicate chat the samples dredged MgO lowest contents, have lower P25 0 from Laysan Island were erupted during than some of the less fractionated lavas, the alkalic eruptive stage. indicating that apatite is also a K/Ar RESULTS fractionating mineral. In summary, we speculate that the Samples for conventional Ar analyses least fractionated Laysan Island lavas weighing from 5 to 1’2 s were cut from were derived from an alkalic basalt hand specimens with a water-cooled by crystallization of mainly olivine diamond saw. An adjacent portion of and clinopyroxene, and that the group each sample was finely pulverized of lavas analyzed represents successive (less than 74 pm) and used for the 39 liquids derived by continued fractionation 0 K 2 measurements. Samples for 40Ar/ Ar of clinopyroxene, plagioclase, titano- total fusion and incremental. heating magnetite, and some apatite in at least analyses were each small cores 6 mm two parent magmas. Table 4 lists some in diameter by 10 cm long, weighing key trace-element ratios in Laysan Island. from 0.5 to 0.8 g. and Northampton Bank lavas,. and in Four K 2 0 measurements were made on basalts from the three principal eruptive each sample by flame photometry after stages of the Hawaiian Islands. The lithium metaborate fusion and disso- average K/Ba ratio of the Laysan Island lution (Ingamells, 1970). Conventional Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 898 TABLE 4. KEY TRACE-ELEMENT RATIOS K/Rb 470 390 530 375 200(?) 450 405 K,'Ba 30 32 39 28.5 3.1 24 25 16A 1 Zr/Y '5. 1 7.3 5.2 7.2 7.2 6.5 7.75 Rb/Sr 0.019 0.031 0.019 --- 0.08 --- 0.024 Ba/Sr 0.30 0.38 0.26 --- 0.69 0.50 0.63 P205/Sr 7.6 8.0 8.0 --- 6.5 9.0 7.8 Data from 'Tables 2 and 3 for Northampton Bank and Laysan Island, from Leeman. and others (1480'fand Bence and others (1981) for Kilauea and Mauna Loa, from Clague and Beeson (1980) for East Molokai, from Clague and others (1981) for Hualalai, and from Clague and Frey (1979; unpub. data, 1980) for the Honolulu Volcanic series of Stearns and Vaksvik (1935). 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Ar mass analyses 39 collector mass spectrometer described ’ for the 4oAr/ Ar experiments were done by Stacey and others (1978) and Sherrill with a Nier-type,.single-collector mass and Dalrymple (1980). spectrometer utilizing analogue data 39 Samples for 4oAr/ Ar dating were acquisition. t sealed in air in flat-bottomed, We have used the new 40K decay and fused silica vials and irradiated at abundance constants recommended by the 1 Winthe core of the U.S. Geological International Unionof Geoloeical Sciences Survey TmGA reactor (GSTR) for from Subcommission of Geochronology (Steiger 25 to 40 hr; they received a neutron arid Jzger, 1977), and all previously dose of approximately 2.5 x 10l8 to published age data discussed or cited 4 x 1OI8 nvt. The effective neutron herein h,ive been converted to these new flux was measured with pur.standard constants. Where appropriate, weighted monitor biotite SB-2. Further details means were used, where weig$ting was by of the GSTR flux characteristics, the the inverse of the estimated variance. monitor mineral, and the corrections This weighting allows data of different for interfering K- and Ca-derived Ar quality to be combined without th< isotopes are given by Dalrymple and poorer data disproportionately affecting Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 900 39 the result. 40Ar/ Ar isochrons were 1978). calculated using-theYork 2 least-squares The three Laysan Island samples on cub* fit with correlated errors (York, which. incremental heating experiments 1969), and the formula recomended by D. were done all gia virtually identical York (Ozima and others, 1977, p. 479) plateau and isochron ages. In general, for the correlation coefficient r. we have been conservative in choosing The calculated ct3nventional K-Ar and which increments to include in the 39 the 40Ar/ Ar ,total fuSorgages for the calculation of the weighted mean plateau Laysan Island samples (Table 5), which and isochron ages. The results, however, fall within the range 18.8 to 21.4 m.y., are not changed significantly by including do not show the severe discordance additional increments in the calculations between these two techniques that is (Table 7). 39 common in samples of highly altered The consistency between the 40Ar/ At submarine basalt (Clague and others, incremental heating, the conventional 39 39 1975). The 40Ar/ Ar incremental K-Ar, and the 40Ar/ Ar total fusion heating results (Table 6, Figs. 3-6) results provides strong evidence that are also indicative of samples with the calculated aaes of the Laysan Island relatively undisturbed K-Ar systems. samples are reliable and reflect These data show age-spectrum plateaus crystallization ages. We consider the for more than 50% of the 39Ar released, weighted mean of 19.9 -I 0.3 m.y. of the concordant plateau and isochron ages, four isochron ages to represent the age isochron intercepts not significantly of the alkalic stage of volcanism on 36 different from the atmospheric 40Ar/ Ar Laysan Island volcano. The weighted value of 295.5, and low values for the mean of the plateau ages (20.4 f 0.3 m.y.) index of fit [SUMS/(n-2)], all does not differ significantly from the characteristic of reliable incremental isochron ages at the 95% confidence heating ages (Lanphere and Dalrymple, level. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 LAYSAN D1-2 hawaiite 1~241k 0.014 10.344 3.626 68.0 20.2 +. 0.4 D1-4 hawaii t e 1.868 f 0'.011 6.367 5.594 46i2 20.7 2 0.4 D1-S mugearite 2.639 k 0.030 7.097 7.173 86.5 18.8 2 0.4 "D1-16 hawaiite 1.648 k 0.026 8.519 4.655 46.4, 19.5 f 0.4 '8.080 0.6392 5-4a thole ii te 0.217 & 0.004 20.7 2 0.6 I 7.128 0.6570 11.713.2 i 5.959 0.4333 5-4b tholei ite 0.222 & 0.005 13.7 2 0.7 t 5.024 0.4633 5.1 8.412 0.5436 5-4c tholeiite 0.182 +. 0.001 19.2 & 1.5 7 -235 0.4709 9.5 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 9 0 2 TABLE 5. (CONTINUED) 40Ar/’gAr ANALYSESb LAYSAN D1-1 hawaiite 0.005891 3.727 3.286 0.00719 c, 12.4 0.2 49.9 19.7 2 0.4 D1.2 hawaiite 0.005891 5.542 3.333 0.0 1280 7.1 0.1 36.5 21.4 2 0.6 D1-4 hhwaiite 0.005678 5.484 1.665 0.01198 j.8 0.1 37.8 21.1 2 0.6 D1-5 write 0.005678 2.913 0.766 0.00532 6.3 0.2 68.2 20.5 2 0.j D1- 16 hawaiite 0.G15678 3.035 2.413 0.00408 16.1 0.2 66.5 20.6 2 0.3 NORTHAMPTON 5.4a tholeiite 0.009174 14.92 19.91 0.0511 10.6 <.1 9.4 23.4 A 2.8 5-4b tholeiits 0.009174 61.60 36.42 0.2159 4.6 <.I 1.2 12. j ~10.3 5 4c tholeiite 0.0091i4 25.69 23.30 0.0896 7.1 <.I 3.9 16.8 5 4.3 a Calculated mean and standard deviation of four analyses. Subscripts indicate radiogenic (R) , calcium-derived !Ca), and potassium-derived (K) argon. -10 -1 -4 C X, + A, = 0.581 x 10 yr, , AB = 4.962 x loblo yr-’, “K/K = 1.167 x 10 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 D1-1 500 1.713 1.213 0.0532 6.3 8.8 0.6 16.5 2 2.3 (J=0.006059) 600 5.81 0.855 0.01288 4.4 35.6 1.8 22.5 2 1.4 700 2.896 0.771 0.00367 23.3 64.5 5.7 20.3 2 0.7 800 2.768 1.469 0.00340 32.2 67.7 11.7 20.4 5 0.6 900 2.299 2.410 0.002 17 14.4 80.2 30.2 20.1 2 0.6 975 3.793 6.391 0.00762 1.9 54.0 22.8 22.3 2 1.3 1050 3.555 15.38 0.009 14 8.1 58.1 45.8 22.8 2 1.0 fuse 5.294 14.89 0.01458 4.2 41.1 27.8 23.8 5 1.5 99.8 Recalculated total fusion age = 20.7 f 1.6 Recalculated 4oArR/39Ar = 1.90 1 Total “ArR = 3.85 x 1051 1 mol/gm D1-4 450 25.27 0.802 0.0765 0.8 10.7 0.3 28.6 5 7.7 (J=0.005891) 525 14.68 ,O.683 0.0419 0.4 16.0 0.4 24.8 6.7 600 4.249 0.745 0.00788 5.4 46.4 2.6 20.9 5 0.8 700 3.031 0.772 0.00375 9.6 65.3 5.6 20.9 0.5 800 3.434 0.720 0.00518 8.2 56.9 3.8 20.7 5 0.6 900 2.472 0.731 0.1865 10.6 79.8 10.7 20.9 5 0.4 fuse 2.301 2.249 0.00198 65.0. 82.1’ 30.8 20.0 5 0.4 100.0 Recalculated total fusion age = 20.4.a l’.O Recalculated 4oArR/3%r = 1.928 Total “[email protected] x mol/gm a. Corrected for 37Ar decay, half-life = 35.1 days. b he +At = 0.58: x lo-’’ yr-1, A0 = 4.692 x 10-l’ yr”, “K/K = 1.167 x mol/mol. Errors are estimates of the standard deviation of analytical precision (Dalrymple and Lanphere, 1971). Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 904 TABLE 6. (CONTINUED) D1-16 450 20.70 1.724 0.0635 2.1 10.0 0.7 22.0 A 3.2 (run 1) 525 15.31 0.867 0.0455 0.5 12.6 0.5 20.4 2 4.5 (5-0.005891) 600 7.79 0.842 0.0197 2.3 26.2 1.2 21.6 2 2.0 700 5.36 0.923 0.01 15 8.5 37.9 2.2 21.4 A 0.9 800 3.705 0.851 0.00605 10.7 53.5 3.8 20.9 2 0.7 900 3.221 0.971 0.00447 8.5 61.2 5.9 20.8 A 0.5 fuse 2.250 2.91 1 0.00198 67.4 84.2 40.1 20.1 A 0.4 100.0 Recalculated total fusion age = 20.4 5 1.0 Recalculated 4oArR/39ArK = 1.932 Total ‘)‘ArR = 5.12 x lo-’ ’. mol/gm D1-16 500 57.0 0.819 0.1833 0.8 5.1 0.1 27.7 A 12.8 (run 2) 600 136.6 0.889 0.4557 6.3 1.4 Recalculated total fusion age = 20.4 f 1.0 Recalculated “ArR I3’ArK = 2.157 Total 40Ard =, 5.11 x 10-l’ mol/gm Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 905 TABLE 6. (CONTINUED) Apparent ageb Temp. 39Ar Sample (OC) 40Ar/39Ar 37A~/39Ara 36Ar/39Ar (%of total) 40ArR 36Arca (lo6 yr) -- NORTHAMPTON -- 5-4a 500 50.3 4.566 0.1613 22.5 5.9 0.8 28.0 2 6.0 (J=0.005281) 600 11.77 5.50 0.0316 31.4 24.5 4.7 27.4 2 2.8 700 9.93 13.40 0.0280 17.3 27.6 13.0 26.1 4.0 800 16.98 11.97 0.0514 6.5 16.3 ‘6.3 26.3 5 7.4 900 29.55 24.36 0.0929 4.8 13.7 7.1 38.8 2 13.5 975 9.41 58.5 .0.0388 8.8 ~ 28.2 41.1 26.0 2 5.5 1050 11.45 107.4 0.0560 5.3 30.8 52.2 35.7 2 7.9 fuse 30.65 125.6 0.1171 20.0 29.2 62.5 2 16.6 100.2 Recalculated total fusion age = 29.4 2 1.5 Recalculated ‘OArR/ 39ArK = 3.107 Total “ArR = 1.11 x mol/gm 5-4c 500 94.7 1.616 0.3122 7.1 2.7 0.1 22.7 5 20.2 (J=0.005281) 600 48.11 3.461 0.1458 6.8 11.0 0.6 50.0 2 13.0 700 39.98 5.755 0.1245 8.4 9.2 1.3 34.6 + 11.1 .2- 800 15.43 6.302 0.0456 35.6 15.9 3.8 23.3 2 4.0 900 12.75 15.63 0.0414 15.0 . 13.7 10.3 16.7 2 6.0 975 30.34 12.47 0.0944 3.6 11.4 3.6 32.9 2 13-7 1050 21.67 18.09 0.0768 5.2 2.0 6.4 40.9 5 11.2 fuse 9.58 81.09 0.0469 -LEL 23.2 47:O 22.2 4.0 100.0 Recalculated total fusion age = 26.2 2 1.3 Recaculated 4oArR/39ArK= 2.769 Total “ArR = 7.32 x mol/gm. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 906 TABLE 7. SUMMARY OF AGE-SPECTRUM AND ISOCHRON ANALYSES OF DATA FROM 40AR/39AR INCREMENTAL HEATING EXPERIMENTS ON SAMPLES DREDGED FROM LAYSAN AND NORTHAMPTON VOLCANOES, HAWAIIAN VOLCANIC CHAIN Age spectrum Isochron Wt. mean Increments age * 39Ar Age SUMS/ 6 (106 yr) intercept (h'-2) Sample used (10 yr) (%I ______.-__-_--..---__------______^__------LAYSAN D1-1 all 20.8 f 0.5 100 20.7 5 0.6 295.3 f 7.5 5.3 600' - 900' 20.4 5 0.4 79.4 19.8 k 0.4 313.7 f 11.8 0.05 4 700' - 900' 20.2 2 0.4 63.6 19.8 5 0.4 305.6 f 30.8 0.06 Dl-4 all 20.6 f 1.5 100 80.0 5 0.2 309.0 6.6 1.2 + 600' - fuse 20.6 k 0.3 98.8 19.9 f 0.3 312.5 f 12.2 1.9 5 D1.16 all 20.4 k 0.9 100 20.1 k 0.2 300.9 2.8 - 0.80 4 (run 1) 700' - fuse 20.4 2 0.3 95.1 19.9 5 0.2 310.9 f 6.3 0.25 D1- 16 all 20.7 r. 2.4 100 20.0 5 1.0 297.5 f 2.3 2.0 n + (run 2) 600' - fuse 20.7 5 2.1 99.2 20.1 5 1.1 297.4 2 2.6 2.4 NORTHAMPTON 5-4a all 28.0 k 3.2 100 27.2 5 2.9 298.0 f 4.1 1.7 500'-! 975' 27.1 2 3.0 91.2 26.3 2.3 297.1 2 4.2 0.23 4 500' - 800' 27.0 2 2.7 77.6 26.6 & 2.7 296.4 2 4.4 0.04 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 907 4Er -- -- -. sorn?ie -i I LhYSAN cl fuse 1 E' jZr 2eee4 . ._ . . ..--_ .- . 1 LAYShN smpie 2;-I i i o vood in fit + rot uoed . I 5; A--yl//+35 Figure 3. Age spectrum and isochron diagrams for 40Ar/ 39 Ar incremental heating experiment on sample DI-l from Laysan volcano. Dashed lines on age spectrum indicate the estimated standard deviation of analytical preciskon about the calculated age (solid lines) of each gas increment. Tempenatures are in degrees Celsius. Argon isotope ratios are corrected for "Ar, 39Ar, and 36Ar derived from undesirable reactions with K and Ca. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 908 1 LAYSAN sample 01-4 E' ...... fka ...... __.______...... ~ .__- 3 C ZZ? 6-tB 3 -4 I 450 1, .I B I I I Figure 4. Age spectrum and isochron diagrams for 40Ar/ 39Ar incremental heating experiment on sample DI-4 fpom Laysan volcano. Symbols as in Figure 2.. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 tI -~ ... - . . IIC . ., 1 ~ ~ 0 2m aa Em? 8ZX 1 E0C Ar-39/Ar-36 Figure 5. Age spectrum and isochron diagram? for ‘‘Ar/39~~ incremental heating experiments on sample D1-16, run 1, from Laysan volcano. Symbols as in Figure 2. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 910 LAYSAN scmple 01-16 run 2 i Ar-39 re! eased. cumul at 1 ve percent LAY SAS - sample 01-16 run 2 105% ,/ 50Q- c) uoed In fit / ,/ + not uoel ,' , ,I t. /, 4DE - L 9Z%,/9Z%, / 4 c sums/cn-21 = 2 43 I 2001 I I I I I a 2Q 40 60 8E 100 1 20 Figure 6. Age spectrum and iaochron diagrams for 4oAr/39Ar incremental heating experiment on sample DI-16, run 2, from Laysan volcano. Symbols as in Figure 2. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 Interpretation of the results for signjficantly different from the atmospheric the shree tholeiitic samples from. value (Fig. 7). We interpret these data Northampton Bank volcano is less to represent an age of crystallization straightforward than for the Laysan and use the isochron age of 26.6 f 2.7 m.y. Island samples. The conventional to represent the age of the Northampton 39 K-Ar and 4oAr/ Ar total fusion ages Bank tholeiitic shield because the range from 13.7 to 23.4 m.y. (Table 5). calculation of the isochron age requires Although the ages obtained by the two no assumption about the initial Ar total fusion techniques on individual composition. Although we have used samples are not statistically discordant, only the first.four of the eight gas owing to the large analytical increments in calculating the weighted .39 uncertainties in the 4oAr/ Ar total mean plateau and isochron ages, the fusion data, the relatively large results do not change significantly if apparent age differences between samples we use additional increments in the suggest that the K-Ar systems in these calculations (Table 7). rocks have been disturbed. This result The age spectrum of sample 5-4c is not surprising in view of previous (Fig. 8) indicates a disturbed system findings that the K-Ar system in Hawaiian and has no plateau. We conclude from tholeiite is easily disturbed by even the data that this sample yields no moderate alteraticm in the submarine useful age information. environment (Dalrymple and others, It is not unusual for Hawaiian lavas 1977). altered in the submarine environment 39 39 Sample 5-4a has a 40Ar/ Ar age to give discordant 4oAr/ Ar total spectrum plateau that includes more fusion and conventional K-Ar agqs and than 75% of the 39Ar released, an yet yield crystallization ages from 39 isochron age concordant with the 40Ar/ Ar Incremental heating experiments plateau age, and an intercept not (Clague and others, 1975; Dalrymple Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 c Ar-39 released, cumulative percent 2001 I I 1 I I a 10 20 30 40 50 Ar-39/Ar-36 Figure 7. Age spectrum and isochron diagram for 'l0Ar/39~, incremental heating experiments on sample 5-)la from Northampton volcano. Symbols as in Figure 2. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 ffi'...;.'~ I I I I I ; I I I I I 1 ~ I I . I Ar-33 re 1 sample 5-4c t I o uiod in fit + not weed 400L (D m I L 280 I I Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 914 and Clague, 1976; Dalrymple and others, geochemically resemble those of the 1980b). As discussed in the papers principal Hawaiian Islands. The cited, this is probably due-to the tholeiitic basalt from Northamptoo Bank, total or near total loss of both which may well derive from a single flow radiogenic 40Ar and K-derived-39Ar, or eruption, demonstrates that tholeiitic the latter by diffusion, recoil, or basalt similar to modern Hawaiia tholeiite both, from the altered parts of'the is present along the Hawaiian Ridge. In rock. A significant advantage of the contrast to the Northampton Bank samples, 39 4oAr/ Ar incremental heating -technique most previously dredged or drilled is that it provides sufficient internal samples of tholeiitic basalt from the criteria, discussed above, to evaluate Hawaiian Ridge are so badly altered the reliability of the result (Lanphere that they are difficult to identify and Dalrymple,. 1978), and it is on this unequivocally as oceanic-island basis that we interpret the data for tholeiite. sample 5-4a as a crystallization age. The volcanic cobbles recovered from Although we have no reason to doubt Laysan Island are all of hawaiite and the reliability of the age of mugearite chemically similar to rocks 26.6 5 2.7 m.y. for Northampton Bank, erupted on the Hawaiian Islands during it is based on results from a single the alkalic druptive stage. These rocks sample and should be interpreted with represent at least two discrete some caution until it is verified by fractionation trends and were derived additional dredging and dating. by crystal fractionation of olivine, clinopyroxene, plagioclase, apatite, DISCUSSION A" CONCLUSIONS and*titanomagnetite from two parent The new data from Laysan Island alkalic basalt magmas in shallow magma and Northampton Bank.show that the chambers. Clague (1974) described lavas dredged from these volcanoes alkalic differentiates dredged from Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 915 several other localities along the is thought to represent the age of the Hawaiian Ridge and southern Emperor main volcanic edifice beneath Northampton Seamounts, and Dalgmple and Garcia Bank. (1980) described samples from JingE The new data bring to 29 the number Seamount in the central Emperor of Hawaiian-Emperor volcanoes for which Seamounts. The abundance of K-Ar ages are available. The data for differentiated alkalic lavas along the the entire chain are summarized in chain suggests that many of these Table 8. We have followed the practice volcanoes evolved to the alkalic of Jackson and others (1972) and used eruptive stage and commonly had shallow the oidest reliable age on shield-building magma reservoirs in which alkalic (tholeiitic) lavas from each volcano basalt parent magmas crystallized for which a significant range in ages and evolved. has been reported, rather than the Because the alkalic stage of youngest (McDougall, 1971) or the Hawaiian volcanoes typically follows average (McDougall, 1979) age. Because the tholeiitic shield-building stage the construction times of Hawaiian by only a few hundred thousand years shields are believed to be only 1 m.y. (McDougall, 1964; Porter and others, or less (McDougall,,1964; Jackson and 1977), the K-Ar age of 19.9 50.3 m.y. others, 1972), the choice of which for the Laysan Island samples is ages to use is probably not critical pi-obably only slightly younger than when treating the chain as a whole, the age of shield construction. The and this uncertainty becomes smaller olivine tholeiite recovered from than the analytical errors at about Northampton Bank is typical of the 20 m.y. For many of the dated volcanoes, tholeiitic basalt that forms the bulk particularly those west and north of of all of the Hawaiian shields, and Northampton Bank, tholeiitic its calculated age of 26.6 f 2.7 m.y. shield-building lavas have not been Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 916 TABLE 8. SUMMARY OF K-Ar GEOCHRONOLOGY ALONG THE HAWAIIAN-EMPEROR VOLCANIC CHAIN Distance From Kilauea Along Volcano H-Ea Best ------Trend K-Ar Age Name Noa (Kilometers) (10 yr) Ref. Remarks + 0.4 Kilauea 1 0 -- Historic tholeiitic eruptions >O - 0.0 Mauna Kea 3 54 0.375 2 0.05 1 Samples from tholeiitic shield (Hamakua Croup) Kohala Mtn. 5 100 0.40 2 0.02 2 Samples from thololeiitic shield (Pololu Volcanic Series) Haleakala 6 182 0.86 f 0.03 3 Age on alkalic basalt (Rula Volcanic Series) W. Maui 8 22 1 1.32 2 0.04 3 Samples from tholeiitic shield (Wailuku Volcanic Series) 'L%nai 9 226 1.28 2 0.04 4 Samples from tholeiitic shield , E. Molokai 10 256 1.52 2 0.05 3 Samples from tholeiitic shield (lower member of East Molokai Volcanic Series) W. Molokai 11 280 1.89 2 0.06 3 Sample from tholeiitic shield (West Molokai Volcanic Series1 Koolau 12 339 2.6 2 0'.1 3,5 Samples from tholeiitic shield . (Koolau Volcanic Series) Waianae 13 37 4 3.7 2 0.1 5 Samples from tholeiitic shield (loher member of Waianae Volcanic Series) Kauai 14 519 5.14 2 0.20 396 Sample from tholeiitic shield (Napali Formation) Niihau 15 565 5.5 2 0.2 7 Samples from tholeiitic shield (unplublished data) Nihoa 17 780 7.2. 2 0.3 8 Samples from tholeiitic shield Necker 23 1058 10.3 2 0.4 8 Samples from tholeiitic shield Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 917 TABLE 8. (CONTINUED) Distance From Kilauea Along Volcano H-Ea Best . ~ --._-_ _----- Trend K-Ar Age Name Noa (Kilometers) (10 yr) Ref. Remarks La Perouse Pinnacle (French Frigates Shoal 1 26 1209 12.0 2 0.4 8 Samples from tholeiitic shield. Laysan 56 1818 19.9 2 0.3 9 Dredged Samples of hawaiite and mugeari te Northapton Bank 35 1841 26.6 2 2.7 9 Dredged samples of tholeiitic basalt Pearl & Hermes Reef 50 228 1 20.6 2 0.5 10 Dredged samples of phonolite, hawaiite & alkalic basalt Midway 52 2432 27.7 2 0.6 11 Samples of mugearite & hawaiite lslands fromconglomerate overlying tholeiitic basalt in drill hole Unnamed 57 2600 28.0 2 0.4 10 Dredged samples of alkalic basalt Unnamed 65 2825 27.4 2 0.5 10 Dredged samples of alkalic basalt, probably frompost- erosional suite Daikaku j i 67 3493 42.4 2 2.3 12 Dredged samples of alkalic basalt Yuryaku 69 3520 43.4 2 1.6 10,12 Dredged samples of alkalic basalt Kimmei 72 3668 39.9 2 1.2 12 Dredged samples of alkalic basalt Koko 74 3758 48.1 2 0.8 13 Dredged samples of alkalic basale trachyte, and ? 6jin 81 4102 55.2 2 0.7 14 Samples of haweiite and tholeiite from DSDP Site 430 Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 918 TABLE 8. (CONTINUED) Nintoku 86 4452 .56.2 5 0,6 14 Samples of alkalic basalt from DSDP Site 403, probably from post-erosional stage. Suiko 90 4794 59.6 2 0.6 16,17 Single dredged sample of mugearite 91 4860 64.7 2 1.1 14 Samples of alkalic basalt and tholeiite from DSDP Site 433 1978). 10 b' - All data have been converted to the new constants A, + At, = 0.581 x 10- -4 yr-', A0 = 4.962 x 10.l' yr -', 'OK /K = 1.167 x 10 mol/mol. . ______.______------References : 1. Porter and others (1977) 10. Clague and others (1975) 2. McDougall and Swanson (1972) 11. Dalrymple and others (1977) 3. McDougall (1964) 12. Dalrymple and Clague (1976) 4. Bonhommet and Others (1977) 13. Clague and Dalrymple (1973) 5. Doell and'Dalrymple (1973) 14. Dalrymple and others (1980b) 6. McDougall (1979) 15. Dalrymple and Garcia (1980) 7. G. B. Dalrymple (unpublished data) 16. Saito and Ozima (1975) 8. Dalrymple and others (1974) 17. Saito and Ozima (1977) 9. This paper _. ____ ...... Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 recovered, and the ages of these volcanoe: near the bend (H. M. Sachs, quoted in are based on the ages of post-shield- Clague and Jarrard, 1973, p. 1138-1139), building lavas. For all of the volcanocs and an early Maestrichtian age for except the unnamed volcano 63 (Table 8), n'annoflora in deposits above basart the samples are from the alkalic eruptive at DSDP Site 192 on Meiji Seamount sfage,/ and the K-Ar ages should be close (Worsley, 1973) at the northern end of to but younger than shield building the Emperor chain. It is evident from ages. The samples from volcano 63 Figure 9 that the age'data substantiate probably are from'lava erupted during the age-distance corollary and provide the post-erosional stage and, by analogy strong support for the general (kinematic) with volcanoes of the principal Hawaiian hot spot hypothesis for the origin of Islands, may bc younger than the main the entire Hawaiian-Emperor chain. An shield by as much as several million unweighted least-squares line through years. the radiometric data, forced through The Hawaiian-Emperor age data are the origin, yields an average volcanic plotted as a function of distance from propagation rate of 8.2 ? 0.2 cm/yr Kilauea in Figure 9. In addition to (Fig. 9). the K-Ar data, we have plotted three Although there is a stiking increase fossil minimum ages for volcanoes for in the age of the volcanoes as a function which no radiometric data exist. These of distance frondKilauea, the increase include an age of 28 to 31 m.y. for is not exactly linear. As Jackson (1976) nannofossils in volcanogenic deposits pointed out, the scatter may be due to at DSDP Site 311 on the archipelagic errors in the age data, to the fact that apron of a volcano 240 km west of different stages of volcanism have been Midway Islands (Bukry, 1975), an age dated on the different volcanoes, to of 39 to 41 m.y. for dredged large real changes in the volcanic propagation benthic foraminifers from Kammu Seamount rate, or to a combination of these factors. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 920 HAVAI I AN-EMPEROR CHAIN age - distance data 1 OJlG A ** r\ I -fi1ntaku .-..- I L Koh% ** rUryaku : i vli .' - R. -r ' a, 40- :+ $7 ! 07 ; awl I 5 *. I L ,+ < NoR~/?/~~~~/&.-Midmy.A A I . I x !I 28 - -'A A o tholeiitio lava ,- LArs/,v A alkolic lovo 1 o poet-arosionol lava I , * * 0 "F F Shoals + fossil doto 0& I I I I I I Figurc 9. Age of volcanoes in thc Hawaiian-Emperor chain as a function of distance from the Kilauca Volcano. Dashed lina (8.2 -+ 0.2 cm/yr) is a least .squ&res fit to tht-rsaiomctric aata forcop through the origin. Data from Tzbla 8. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 Certainly, errors in dating contribute and the cessation of the alkalic stage some uncertainty to the results. While of volcanism is always 1 m.y. or less. the deviations from linearity are too If our assuption is correct, then the great to be accounted for entirely by scatter due to this difference is small. analytical errors, most of the samples Extensive chemical studies and drilling recovered by dredging and drilling (Jackson and others, 1980) have shown (that is, from Laysan Island to Suiko that the volcanoes in the Hawaiian-Emperor Seamount) are altered to some degree chain follow the same eruptive sequence 39 and are datable only by 4oAr/ Ar observed in the principal Hawaiian Islands. incremental heating techniques that We are uncertain, however, that the timing are thought to provide sufficient of the successive stages applies with internal checks to identify unreliable equal validity throughout the entire data. There may be, however, factors volcadc chain, although dating of both 39 in 4oAr/ Ar dating of lavas altered tholeiitic and alkalic lavas from Ojin in the submarine environment that are and Suiko Seamounts (Dalrymple and others, not adequately understood, and it is 1980b) suggests that it probably does. possible that the data set contains Thus, some of the scatter in the ages a few incorrect ages. may.be due to larger than anticipated Petrographic and chemical data show differences in age between tholeiitic that the age data are from lavas erupted and alkalic volcanism, although it. seems during different stages, and thus at unlikely that this factor can explain different times, in the life cycles of all of the irregularities in the data. the volcanoes. On the basis of the Real short-term changes in the &ronology of the well-studied Hawaiiaq volcanic propagatibn rate were first shields, we have assumed that the age proposed by Jackson and others (1972) difference between the inception of to account for the observation that the tholeiitic shield-building volcanism age-distance data for the volcanoes of Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 922 the principal Hawaiian Islands are due partly to nonlinear volcanic nonlinear and indicate an acceleration propagation. The present data of propagation during.the last 5 m.y. indicate, however, that nonlinear or so. Shaw (1973) and Walcott (1976) propagation should be retained as a proposed thermal 'feedback and mechanisms working hypothesis. to account for such short-tern variations. ACKNOWLEDGMENTS Short-term nonlinearity has been disputed by McDougall (1979), who argued that We thank J. Saburomaru, S. E. Sims, the depa,rtures from linearity along the B. M. Myers, and J. C. VonEssen for Hawaiian segment of the chain are assistance with the argon measurements; explainable solely by dating errors J. H. Tillman and P. R. Klock for.the and by differences in the volcanic stage potassium measurements; and P. G. Helfer sampled. Our new Laysan Island and and the staff of the U.S. Geological Northampton Bank data strongly suggest Survey Reactor Facility for the fast that the volcanic propagation rate may neutron irradiation of the samples. not be exactly linear. The distances We also appreciate the helpful manuscript of these two volcanoes from Kilauea reviews by our colleagues R. A. Koski, differ by less than 25 km (Table 8). R. T. Holcomb, S. 0. Schlanger, and At a uniform propagation rate of 8 to 9 E. Epp. This work was supported in cmlyr, theiuges should differ by only part by the Office of Naval Research. about 0.28 to 0.32 m.y. instead of the 6.7 m.y. indicated by the'measured ages. A similar discrepancy occurs in the ages of volcanoes near the bend (Fig. 9). More detailed age data will be needed before we know whether these age-distance irregularitites are Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 923 APPENDIX: SAMPLE DESCRIPTIONS NORTHAMPTON BANK LAYSAN ISLAh?] 5-4a Tholeiitic basalt. Intergranular D1-1 Hawaiite. Sample has subtrachytic to interstitial textured olivine texture and contains rare pheno- porphyritic basalt. 01 ivine crysts of augite, Fe-Ti oxides, and phenocrysts (10%) as large as olivine; and microphenocrysts of 3 x 7 mm have greenish-brown plagioclase in a groundmass of 45% saponite alteration on fractures plagioclase (An52), 20% augite, 22% and rims of most grains; and opaque Fe-Ti oxides, 11% srnectite picotite and opaque inclusions after glass, olivine, plagioclase, in a groundmass of 358-408 very very rare biotite, and 2% vesicles. pale brown augite, 30% plagioclase Fe-Ti oxides are commonly rimed by 1, (An 60-68 20%-25% opaque Fe-Ti hematite. Average grain size is oxides, and <5% glass mostly 0.05 mm. altered to smectite. Average D1-2 Hawaiite. Sample has hyalopilitic groundmass grain size is 0.1 mm. texture and contains rare pheno- 5-4b Tholeiitic basalt. Like 5-4a crysts of plagioclase and olivine except that some olivine pheno- in a groundmass of 44% plagioclase, crysts are concentrically zoned 26% opaque Fe-Ti oxides, 26% &d kink-banded. Average ground- clinopyroxene, 4% smectite after mass grain size is 0.1 mm. glass, and rare biotite. Average 5-4c Tholeiitic basalt. Like 5-4a grain size is 0.01 mm. except that olivine phenocrysts D1-3 Hawaiite. Sample has intergranular as long as 6 mm make up 10%-15% texture and contains rare pheno- of the rock. Average groundmass crysts of plagioclase and olivine grain size is 0.1 m. in a groundmass of 60% plagioclase, 26% opaque Fe-Ti oxides, 2% augite, Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 -.- .__ -- 4% olivine (iddingsite), 5% L5% plagioclase, 15% augite, 17:: vesicles, and 4% clays. Average opaque Fe-Ti oxides, 2 3% srrec t i :e, grain size is 0.05 mm. rare biotite, and apatite. Average D1-4 Hawaiite. Sample has subtrachytic grain size is 0.3 m. texture and contains rare pheno- D1-7 Mugearite. Sample has hyalopi1i:ic crysts of plagioclase, Fe-Ti oxides to feltv texture and contains and olivine in a groundmass of microphenocrysts of plagioclase, 44% plagioclase, 28% augite, 26% opaque Fe-Ti oxides, and olivine Fe-Ti oxides, and 2% smectite in a groundmass of 52% plagioclase, after glass, and rare biotite. 11% augite, 155: opaque Fe-Ti oxides, Olivine is altered to iddingsite. 8X olivine (iddingsite), 2% vesizles, Average grain size is 0.02 mm. and 12% smecite. Average grair. D1-5 :4ugearite. Sample has hyalopilitic size is 0.01 m. to felty texture and contains D1-8 Haciaiite. Sample has subtrachy:ic rare phenocrysts of plagioclase . texture and contains phenocrysts in a groundmass of bl% plagioclase, of plagioclase and opaque Fe-Ti 22% augite, 17X opaque Fe-Ti oxides oxides in a groundmass of 36% 5% olivine, 5% vesicles, and 10% plagioclase,.20X augite, 252 opzGue smectite. Smectite oicures both Fe-Ti oxides, 19% smectite, an6 as vesicle fillings and as rare apatite and olivine replacements of glass. Olivine (iddingsite). Plagioclase is is replaced by iddingsite. partially altered to smectite. Average grain size is 0.02 mm. Average grain size is 0.01 mm. D1-6 Hawaiite. Sample has subtrachytic D1-9 Yugearite. Sample has hyalopilitic texture and contains phenocrysts texture and contains rare pheno- of opaque Fe-Ti oxides and rare crysts of opaque Fe-Ti oxides and plagioclase in a groundmass of microphenocrysts of plagioclase in Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021 925 a groundmass of 35% plagioclase, litic texture 2nd contains 11% augite, 22% opaque Fe-Ti phenocrysts of plagioclase, opaque oxides, 4% olivine (iddingsite), Fe-Ti oxides, and olivine 14% vesicles,, and 14% smectite. (iddingsite) in a goundmass of Average grain size is 0.01 mm. 55% plagioclase, 6% augite, 21% D1-10 Mugearite. Sample has hyalopi- opaque Fe-Ti oxides, 5% olivine litic texture and contains pheno- (iddingsite), 3% vesicles, 10% crysts of plagiocl-ase and opaque smectite, and rare apatite. Fe-Ti.oxides in a groundmass of Average grain size is 0.01 mm. 55% plagioclase, 19% augite, 15% D1-14 Hawaiite. Sample has hyalopilitic opaque Fe-Ti oxides, 1%olivine to intergranular texture and con- (iddingsite), 1% vesicles, 9% tains phenocrysts of. plagioclase smectite, and rare apatite. and olivine (iddingsite), and Average grain size is less than microphenocrysts of opaque Fe-Ti 0.01 m. oxides in a groundmass of 38% D1-11 Mugearite. Sample has hyalopi- plagioclase, 28% augite, 25% litic texture and contains pheno- opaque Fe-Ti oxides, 2% olivine crysts of plagioclase and (iddingsite), 7% smectite, and microphenocrysts of opaque Ye-Ti rare apatite. Average grain size oxides in a groundmass of 43% is 0.01 mm. plagioclase, 23% augite, 17% D1-16 Hawaiite. Sample has subtrachytic opaque Fe-Ti oxides, 17% texture and contains phenocrysts smectite, rare olivine of plagioclase in a groundmass of (iddingsite), and rare apatite. 31% plagioclase, 41% augite, 25% Average grain size is less than opaque Fe-Ti oxides, 2% smectite, 0.01 mm. and rare apatite. Average grain D1-12 Mugearite. 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Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/92/6_Part_II/884/3444469/i0016-7606-92-6-884.pdf by guest on 25 September 2021