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Petrology And. K-Ar Ages of Dredged Samples'from Laysan Island And

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Petrology And. K-Ar Ages of Dredged Samples'from Laysan Island And 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 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 -885 160' '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. 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 886 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 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 887 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, 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 888 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. 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 889 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.
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