SOUTH PACIFIC ISSN.OllO-0408

MARINE GEOLOGICAL NOTESTECHNICAL SECRETARIAT Vol. 3 No.4CCOP/SOPAC, SUVA May 1989

OBSERVATIONS ON THE BATHYMETRY ANDGEOLOGY OF THE NORTHEASTERN MANIHIKIPLATEAU, SOUTHWESTERN PACIFIC OCEAN

Helmut BeiersdorfBundesanstalt fur Geowissenschaften und Rohstoffe,

Stilleweg 2,3000 Hannover 51,Federal Republic of Germany

Jorg ErzingerInstitut fur Geowissenschaften und Lithospharenforschung,

Senckenbergstrasse 3, D-6300 Giessen,Federal Republic of Germany

ABSTRACT

An area of 1,800 km2 situated about 60 kmnorthwest of Rakahanga (Cook Islands) on thenorth-eastern slope of the Manihiki Plateau wassurveyed by RV Sonne using a multibeam echo-sounder, a 3.5-kHz subbottom profiler, dredges, andcorers. Where the High Plateau of the ManihikiPlateau is separated from a broad midslope terraceby an escarpment, the basaltic basement and anoverlying, 260-m thick volcaniclastic sequence areexposed. Both were cored at DSDP Site 317, about200 km SSW of the Sonne survey area. The outcropsof these volcaniclastic sediments, together with theoverlying lower Eocene chert-bearing chalk andupper Eocene-lower Miocene chalk on the escarp-ment were mapped. The thickness and areal distri-bution of the volcaniclastic sediments suggest thatsignificant explosive events took place in this regionduring the Early Cretaceous.

The detailed bathymetric mapping revealedtwo ENE-·trending canyons 12 km long and 300 mdeep that cut into the High Plateau. The canyonsseem to have resulted from block faulting of thebasement.

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INTRODUCTION solutions were reduced and copper precipitated. Thevolcaniclastics contain only traces of sulfur, whichwould indicate that the sulfur in the hydrothermal

A number of large plateaus rising from the solutions was precipitated in the basalt beforePacific Ocean floor have been little explored. Most of reaching these sediments, resulting in thethem rise 2-3 km above the surrounding seafloor. chalcopyrite found in the underlying basalt. TheThey include the Ontong Java Plateau, the Shatsky source of the sulfur could be the circulatingRise, the Magellan Rise, and the Manihiki Plateau. seawater, the formation water of the oceanic crust,The Manhiki Plateau (Figure 1A) has a volcanic or the upper mantle (Rona, 1978; Cann et al. 1983).structure similar to that of Iceland and, according to Other minerals in the Manihiki Plateau also point toWinterer et al. (1974), is a relict of an extinct spread- the existence of a convective hydrothermal system,ing centre near the triple junction (intersection of e.g., analcime and calcite filling voids.the spreading centres) between the Pacific,Antarctic, and Farallon plates (Figure 1B). This Copper is distributed through the entirewould also explain the unusual thickness of the volcaniclastic sequence at site 317A. It is uncertainbasaltic oceanic crust beneath the Manihiki Plateau whether the mineralisation process continued(see also Larson, Smith, and Chase 1972). throughout the entire period of formation of the

sequence. Mineralisation certainly occurred atAccording to Winterer et al. (1974), the repeated irregular intervals. Evidence ofthis apears

spreading centre was formed during the Barremian in the frequent termination of clay seams (which(Early Cretaceous). This has been confirmed by probably were the paths of ascer : for the hydro-radiometric age determinations of 106 ± 3.5 Ma. thermal solutions) at bedding planes. This could(Lanphere and Dalrymple 1976). According to mean that copper-bearing solutions flowed out ontoSchlanger et al. (1976), the spreading centre was the seafloor. Thus, on the Manihiki Plateau,active for 10-20 m.y. hydrothermal activity was probably continuous for

the entire period of accumulation of the volcani-In the neighbourhood of the spreading centre, clastics rather than only briefly at the end of the

besides the eruption of basaltic lava, volcaniclastic volcanic activity. This also means that relativelyrocks were deposited in relatively shallow water large copper deposits could have been formed in the(-400 m to ?subaerial). In the area of Deep Sea plateau, similar to those observed at currentDrilling Project (DSDP) Hole 317A, these rocks spreading centres (e.g., Red Sea and Juan de Fucaconsist of a green-black zeolitic sandstone and Ridge, Bischoff, 1969, Backer, 1976, Davis et al.siltstone sequence ca.240 m thick, sometimes tra- 1987). The entire area cf volcaniclastics can beversed by thin red-brown clay seams. The series is viewed as prospective for copper.underlain by mid-ocean ridge basalt (MORB). In allparts of the borehole, the volcaniclastic sediments The seismic-reflection records (e.g., Figure 2)contain native copper with an average content of150 show that the .volcaniclastics are widely distributedppm (6 analyses). One analysis yielded a value of under the high part of the Manihiki Plateau and cropseveral thousand ppm Cu. Chalcopyrite was found in out at an escarpment on the northeast edge of thethe underlying basalt. plateau. According to Winterer et al. (1974), this

escarpment marks a fossil transform fault where aNative copper and chalcopyrite are not Cretaceous spreading centre was offset and it is

unusual in oceanic basalt. They were recently highly probable that this spreading centre was notidentified in DSDP Hole 597B in the East Pacific limited to a narrow zone but consisted of several(18°48.4'S, 129°46.2'W) and during RV Sonne cruise eruption centres distributed over a wide area. ThisSO-26 in the same general area (Marchiget al.1986). would mean that the volcaniclastics cover a largeChalcopyrite also occurs in active hydrothermal area. Whether DSDP Hole 317A is located in thesystems, e.g., the metalliferous brines of the Red Sea middle of a former eruption centre is not clear ..(Bischoff, 1969) and DSDP Hole 504B on the southside of the Costa Rica Rift (Cann et al.1983). Winterer et al. (1974), in one of their

. interpretations (Model Il), place the former spread-Jenkyns (1976) concluded that the native ing centre at the outcrop of acoustic basement

copper in DSDP borehole 317A is of hydrothermal southeast of DSDP Site 317. lfthis model is accepted,origin. The copper probably was leached by seawater then the best chances of finding the volcaniclasticsfrom the fissures and hollows of the hot basalt and are on the northeast and southwest flanks of thetransported as a chloride complex into, the overlying High Plateau near the spreading centre.volcaniclastic sediments. The clay seams thattraverse the volcaniclastics could mark the transport lfthe eruption centres were close together andpaths (Jenkyns, 1976). On contact with calcite and evenly distributed over a large area, then minera-?hematite in the volcaniclastics, the copper-bearing lised volcaniclastics would be expected to crop out all

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along the flanks of the High Plateau. The seismic- Bathymetric Observationsreflection records indicate that good outcrops shouldbe found on the northeast slope (Figure 2). Our survey area lies on the northeastern slope

. . . , of the High Plateau, the shallow region between.wIth this evidence the Federal Institute for Manihiki Island and Suvarov Island (see Figure 1).

G~osclences and Natural Resources (BGR) sub- The High Plateau is one of three main bathymetricrnitted a proposal to the Federal Ministry of provinces which make up the Manihiki Plateau AtResearch and Technology (BMFT) to investigate the th th t I f th H' h PI t 'th

rth t fl k f th M ihiki PI t f th e nor eas ern s ope 0 e Ig a eau eno eas an 0 e am 1 1 a eau or eP e f beari I' I ti Th RV seafloor descends from the top of the plateau, at ar sence 0 copper- eanng vo came as ICS. e 'Sonne would be used to (1) conduct a bathymetric dep~h of around 2,500 m, to the central basin ofthesurvey of about 20 x 20 nautical miles (ca. 1,372 km2 Pacific Ocean, at around 5,00? m. The slope is inter-around 9°30'S, 161030'W, using a 3.B-kHz subbottom rupted by an escarpment wh~chma:ks the p~ateau-profiler, and (2) collect samples with a piston corer ward boundary of.a 300-km WIdehor-izontal midslopeand a rock dredge. Sedimentological and geo- terrace. The gradIent. between tohetop of the plateauchemical parameters would be determined and the escarpment IS about 1 . The slope betweenimmediately on board to identify the volcaniclastics the northeast edge of the terrace and the foot of theas soon as possible and thus organise the sampling Manihiki Plateau is steeper than the upper slopemore effectively. The survey was carried out, 20 (2°).Our bathymetric survey was centred on the partNovember - 5 December 1984. of the escarpment crossed by the track of the Glo-

mar Challenger between DSDP Sites 316 and 317RESULTS (Figures 1 and 2). The results ofthe survey were pre-

sented in the form of bathymetric charts with a 20-mThe bathymetry of the survey area was contour interval (Beiersdorf and Erzinger, 1986). A

mapped at a scale of 1:20,000 with contour interval bathymetric map of the survey area with a 100-mof 10m from the data collected along 1,650.6 km of contour interval was prepared from these detailedgeophysical profiles with the multibeam echo- charts. This forms the basic map of Figures 3, 4 andsounder Seabeam and a 3.5-kHz subbottom profiler. 10.A total of 50 kg of manganese nodules and crustswere recovered, as well as 56.65 m of sediment cores. The escarpment was traced across the entireIn addition, a 3-km hydrographic cross section was survey area, Between longitudes 161°38'W andconstructed from data collected with a hydrographic 161°28'Wit trends northwest. At longitude 161°28'Wmulti-parameter probe. Geophysical tracks and sam- the general trend of the escarpment becomes north-pIing stations are shown in Figures 3 and 4. south. The steepest part Ires at a water depth this

between 3,820 and 4,100 m. The average gradient Acoustic Stratigraphyhere is about 25°. This is in agreement with the obser-vation ofWinterer et al. (1974, p. 803) who report a In order to calibrate our 3.5-kHz subbottommean slope of 20° for the main scarp of the High profiler records, we approached the survey area byPlateau. The slope of the upper part of the escarp- crossing DSDP Site 317 and steaming along the linement, between 3,820 and 3,900 m, is relatively of the air-gun profile obtained by the Glomar Chal-gentle and the lower (3,900 - 4,150 m) part steeper. Lenger when she moved from Site 316 to 317 (FiguresThe face of the escarpment is cut by numerous val- lA and 2). At Site 317 no reflectors comparable withleys and two prominent canyons. The canyons cut those in the DSDP air-gun profile were recognisableback into the plateau for about 12 km and as much as in the Sonne 3.5-kHz record. Instead, we observed a350 m deep. The canyons display the steepest gradi- 40-ms wide band of densely spaced reflectors directlyents measured in the survey area, i.e., 50° in the underlying the seafloor. The band increases in refle-southern canyon. It is interesting that the upper ctor frequency between 15 and 20 ms below the sea-ends of the canyons veer from a nearly east-west floor (b.s.f.), Taking an average velocity of sound astrend to a northeasterly one. Valleys and spurs often 1,820 mls (see Schlanger et of. 1976, p.179) the totalfollow th e same northeasterly trend. The escarpment thickness of the bad would be equivalent to 36 m.itself'shows a step at 4,000 m water depth in the Further to the northeast along the Glomar Chal-southeast and 4,120 m in the northwest, that is lenger profile, the depth of penetration of acoustictraceable for long distances ("B", see Figures 6 and signals increases, reaching as deep as 130 ms. Tak-7). A flat, slightly basin ward-dipping terrace at ing the average velocity of sound as 1,820 mls as4,180 m lies beyond the escarpment (Figure 3). At above, this would be equivalent to 118 m. Erosionvarying distances from the foot of the escarpment, a has caused the absence of much of the upper part ofnarrow V-shaped valley 20-30 m deep is developed the sedimentary sequence. This can be judged from(Figures 7 and 9). The terrace is further interrupted Glomar Challenger's air-gun profile betweenby a 200-m high hill in the northwest ofthe survey 10040'S/162°03'W and the escarpment at 9°30'S/area where the escarpment has more irregular relief 161°30'W (Figure 2), and is seen in the 3.5-kHz pro-than in the southeast (Figure 3). files, too (Figure 5).

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The most prominent reflector "e" in the DSDP fore occur on the escarpment at a water depth of ca.air-gun record can be directly correlated with a dis- 4,100 m (equivalent to 475 ms below reflector "e"),tinct reflector in the Sonne 3.5-kHz records, here There is indeed a marked step CD", see Figures 6also called "e". At DSDP Site 317, "e" was detected at and 7) or increase in slope angle at this depth,a subbottom depth of 395 ms (= 358 m b.s.f.). obviously related to the cropping out of erosion-Schlanger et al. (1976) assigned this reflector to an resistant basalt (Figures 6 and 7). Another breakunconformity which separates lower Eocene cherty ("v", see Figures 6 and 7), about 260 m above thechalk from upper Eocene-lower Miocene chalk. The sediment-basalt boundary, was correlated with thereflector is associated with a break C'e", see Figure 6) upper boundary of the volcaniclastic sediments.in slope on the upper escarpment.

The acoustic character of the terrace justA prominent band of reflectors 120-200 ms below the escarpment was not investigated in great

above "e" may be equivalent to reflections between detail, but some observations bear directly on the170 and 275 ms b.s.f. in the air-gun record at Site geology of the escarpment. The subbottom317. This band shows up as a series of closely spaced reflections of the terrace end abruptly at the foot ofreflections. According to the drilling results they are the escarpment (Figure 7), suggesting that therelated to upper Eocene-middle Miocene chalk. The escarpment was caused by faulting and hencestrongest reflector C'd"), which occurs between 225 verifying that the terrace is a structural feature asand 238 ms b.s.f., obviously marks the boundary postulated by Schlanger and Winterer, (1976). Thebetween ooze (upper-middle Miocene), and firm ooze 3.5-kHz records from the terrace, like those from theand chalk (upper Eocene - lower Miocene). It is seen higher parts of the northeast flank of the Highin some of the 3.5-kHz subbottom profiler records Plateau, show erosional scars and signs of re-(Figure 6). deposition. Between 30 and 100 ms b.s.f. there is a

strong reflector C's", see Figure 6), which probablyThe DSDP reflector at 870 ms was not represents an erosional unconformity. The sequence

detected by 3.5-kHz profiling. It marks the interface above the reflector thins and stratification di-between the Maastrichtian and Aptian sequence of sappears with increasing distance from the escarp-limestone, volcaniclastic sandstone, siltstone and ment. The erosional character of the terrace isclaystone, and the underlying basalt. Altogether particularly well seen at the mouth of the canyons552m of sediment separate "e" from the top of the and downstream, where channels cut into thebasalt. The "outcrop" of this reflector should there- sequence down to about 30 ms (Figure 7). The

40

channel which extends eastward from the northern Lithologic Observationscanyon is sediment filled. At the foot of the escarp-ment, a bulge on the seismic profiles consists of seis- The degree of submarine weathering of allmically semi-transparent material that sometimes rock samples obtained by coring and dredging wasshows diffuse reflections and possibly represents an high. From chemical analyses and X-ray diffractionaccumulation oftalus (Figure 7, ?slump deposit). The (XRD) measurements, however, we were able tohill about 3.5 km northeast of the mouth of the determine the original rock type with reasonablenorthern canyon rises about 200 m above the accuracy.surrounding seafloor (Figure 3) and shows a diffuseseismic character with hyperbolic reflections. This is Basaltthe typical seismic pattern ofbasaltic basement witha thin and patchy draping of sediment. Dredge haul 17 KD (Figure 4) consisted of

light grey, greenish-grey, yellowish-grey, and red-Reflector He"was used to determine the strata dish-brown rock fragments, some extremely vesicu-

and hence the block between the two canyons dips lar. The grey varieties were analysed chemicallygently to the southwest (Figure 8). The northwest (Table 1).X-ray diffraction analysis of sample 17 KDboundary of the block, i.e., the northern canyon, BGR 1, which was a light grey fragment, showed X-seems to be faulted. A midslope fault with a small ray amorphous components (?glass), smectite, andcanyonward downthrow as well as the canyonward ?nontronite as major constituents, and feldspar anddip of strata can also be observed (Figure 8). Faulting quartz as minor or trace constituents. Since themay also have been responsible for the 50-70 m chemical and mineralogical composition of the frag-depth increase of the midslope break C'v", see Fig- ments suggest a basaltic origin, and since theures 6 and 7) from ca. 3,800 m, to the east of samples were dredged from the steepest part of the16P31 'W, to water depths of more than 3,900 m to escarpment (water depth> 3,950m) above the acous-the west of this longitude. tic basement, we believe that the samples represent

basalt which was strongly altered by interactionThe interpretation of morphologic features, with seawater. Enrichment in potassium and H20 as

and seismic-reflection observations is given in Fig- well as depletion in calcium also suggest this mode ofure 9. Seismic-reflection facies types, inferred Iithol- origin. Similar samples were recovered from stationsogies, faults, strike, and dip of beds are mapped in 7,9,11, and 12 (Figure 4, Table 1).Figure 10.

Volcaniclastic Sediments and 4,150 m, which includes the steepest part oftheescarpment.

Volcaniclastic sediments, which form the The only volcaniclastic samples without oxidelowermost unit of the sedimentary sequence at coatings were found at station 12 KL (4,138 m;DSDP Site 317, were also recovered from the Figure 4). They were part of a breccia made up ofescarpment during SO 35-1. Here they occur mainly volcaniclastic sediments and other lithologies suchas fragments completely coated with manganese- as chert and basalt. The volcaniclastics are vari-oxide, showing that they were detached from out- coloured volcanogenic sandstones and siltstones.crops before sampling. All volcaniclastic sediments One of the sandstone fragments showed tiny tubessamples came from water depths of between 3,830 coated internally with white minerals, possibly

43

nontronite and phillipsite of hydrothermal origin. nodules are lowgrade since Cu + Ni + Co is usuallySome of the fragments investigated in detail are of less than 1%. In particular, the Cu and Ni values arevolcanic origin (Table 2). The average chemical com- low compared to those of the nodules from areasposition of the volcanigenic sediments found at southeast of Hawaii ("Nodules Belt") which willDSDP Site 317 was compared to that of the SO 35-1 probably be the first ones to be mined. There, Cu andsamples as determined on board RV Sonne by X-ray Ni combined are invariably as high as 2-2.5% (vonfluorescence analysis (Table 3). Except for Mg and Stackelberg and Marchig, 1987).Ca, the composition of the samples from area SO 35- The lithologic interpretations were incorpo-1 is-very similar to those from the DSDP site. MgO is rated in Figure 9.higher in the Site 317 average while CaO is consid-erably" lower. The CaO values in our samples mayresult from contamination with pelagic sediments CONCLUSIONSduring downslope transport after the volcaniclasticsediments were detached from their outcrops. The Volcaniclastic sediments found at thelow MgO content in the SO 35-1 samples lies well northeast margin of the Manihiki Plateau arewithin the wide range of that component in the equivalent to those overlying the basaltic oceanicDSDP samples. The values for some of the minor crust in DSDP Hole 317A in the centre of the Highelements in the SO 35-1 volcaniclastic samples do Plateau of the Manihiki Plateau.not depart significantly from those shown inJenkyns (1976). Our determinations gave: Sr 300 The volcaniclastics occur in talus deposits atppm, Zn 100-250 ppm, Cu 150-250 ppm, Ni 80 ppm, the bottom of an escarpment that separates theand Co 40 ppm. Similar to the volcaniclastic sedi- upper slope of the High Plateau from a midslopemerits at the DSDP site, the SO 35-1 samples re- terrace. The escarpment probably was formed bysemble altered ocean floor basalts, particularly in faulting and exposes not only the volcaniclastic layerthe enrichment in ~O, Ti02, and Sr, and their low but also the basaltic basement. The outcrops wereMgO values (see Table 1, altered basalts). strongly altered by seawater and erosional

processes.Manganese Nodules and Crusts

Seismic and bathymetric data from our surveyAll the successful dredge hauls contained suggest that the thickness of the volcaniclastic layer

manganese nodules and crusts (Figure 4). The crusts is approximately the same as at the drill site, i.e.,cover fragments of rock or indurated sediment. The 260 m. Since the material contained no datablemineralogical and chemical compositions of a num- fossils, the age of the volcaniclastics remainsber of these nodules and crusts are presented in uncertain, but, according to the seismic reflectionTable 4. profile (Figure 2), it should not differ from that

The investigated crusts and nodules are rich determined for the volcaniclastic sediments from thein Fe and fall in the field of hydrogenetic nodules drill site, i.e., Early Cretaceous (Barremian - Aptian)according to the classification scheme of Bonatti (Schlanger et al., 1976).(1981). Their mineralogical composition shows nosignificant difference from "average" hydrogenetic Native copper, which was found in DSDP Holemanganese crusts or nodules. Low Mn and Fe val- 317A, was not observed in the SO 35-1 area. If itues, and the occurrence ofquartz and apatite suggest were ever present, it certainly would have beenthat sample 5KLMA3 was certainly contaminated by leached out long ago. The absence of copper in thepelagic sediment. samples, however, does not preclude hydrothermal

No information was obtained on the distri- activity during the deposition ofthe volcaniclastics.bution ofnodules because they were obtained only in The drusy precipitates of?nontronite and phillipsite,cores and dredged material. Economically, the which were found in the altered basalt and

44

volcaniclastic sediments, may have a hydrothermalorigin.

The same rock types found in the SO 35-1 areaand in Hole 317A were dredged from the easternscarp of the High Plateau during CATO, Leg 3 (seeWinterer et al. 1974). The three occurrences nowdelineate a triangle of considerable size for thepossible occurrence of the volcaniclastic sediments.The low-amplitude magnetic anomalies all over theHigh Plateau indicate a more-or-less uniformdistribution of volcaniclastic sediments in the area(Winterer et al. 1974).

The widespread evidence for Cretaceousvolcanic activity in the western Pacific has beensummarised by Rea and Vallier, (1983). Their datashow that most Cretaceous volcanism occurredduring two separate episodes in the middle and lateparts of the period (110 - 95 and 80 - 65 Ma). Themost significant pulse older than 110 Ma is the oneduring about 120 to 115 Ma, during which thevolcanic crust of the Manihiki Plateau was formed byseafloor spreading (Schlanger et al. 1976). Wintereret al. (1974) developed models for the creation of theManihiki Plateau by seafloor spreading, but alsorealised that drawing conclusions from structuraltrends is precarious because the plateau is clearlynot a normal section of oceanic crust. The role of thetectonic features in the SO 35-1 survey area must beseen in this context.

The escarpment clearly marks the plane of afault, perhaps an ancient transform. The role of thetwo canyons, however, is not clear. The tilting of theblock between the escarpment and the canyonssuggests that the canyons are tectonic in origin. It ispossible that the escarpment and the canyons reflectthe block-faulted structure of the basement createdduring spreading and reactivated during the latertectonic phase, perhaps when the structural terracedeveloped. In this case the canyons could have beenformed by erosion of the fault breccias by bottomcurrents.

The bending of the upper parts of the canyonsmay be due to a strike-slip motion in a northeasterlydirection.

Hydrogenetic manganese nodules and crustsare indicators of a low sedimentation rate. Theirabundance along the escarpment indicates that suchconditions have prevailed for some time. The 1-3 mmthick oxide layers coating rock fragments detachedfrom the outcrops provide a minimum age for theescarpment. Assuming accretion ofmanganese oxideat a rate of1 mm/m.y., then the minimum age of theescarpment would be 1 to 3 Ma. The same minimumage can be taken for the onset of erosion of thecanyons. A conceptual diagram of the geology of theescarpment is given in Figure 9. From our obser-

vations on bathymetry and seismic and lithologic in a sedimented rift valley, northern Juan defacies, a geological map was drawn (Figure 10). Fuca Ridge. Earth and Planetary Science Letters,

82: 49-61.

ACKNOWLEDGMENTS JENKYNS, H.C. (1976): Sediments and sedimentaryhistory, Manihiki Plateau, South Pacific Ocean.

Th th t f I t th G t f Page 873-890 in Schlanger, S.O.; Jackson, E.D.;e au ors are gra e u 0 e overnmen 0 . . . .

th C k I I d c. idi th . t f et al . Initial Reports of the Deep Sea Drillinge 00 s an s lor provi mg e assls ance 0 . .

V it t' T duri . SO 351 II c Project, 33. Washington, D.C., Governmentai 0 I upa urmg cruise - , as we as lor P . ti Offiti .. t k' thei E I . rin mg Ice.gran mg permission 0 wor in err xc usive

Economic Zone. LANPHERE, M.A.; DALRYMPLE, G.B. (1976): K-Arages of basalts from DSD P Leg 33: Sites 315 (Line

The authors are also grateful to Florence I I d) d 317 (M ihiki PI t ) P. . s an $ an anI I I a eau . ageWong of the Branch of Pacific Marine Geology, U.S. 649-653' S hI SO' J kED' t lG I . ISM 1 P k C lif h in c anger, . ., ac son, . ., ea.,eo ogIca urvey, en 0 ar, a Ilorma, w 0 . . . . . .

. d fhi d . d it b t ti II Initial Reports of the Deep Sea Drilling Project,reviewe .ms paper an Improve I su s an ia y. 33 W hi gt D C G t Pri ti. as m on, .. , overnmen rIn mg

Particular thanks go to the CCOP/SOPAC Office.Tthe.chnicaklSecretariat for its continuous support of LARSON, RL.; SMITH, S.M.; CHASE, C.G. (1972):

IS wor . M . li ti f E I Ct'agnatic mea IOns 0 ar y re aceous age in

J E hi th k t th D t h the western equatorial Pacific Ocean. Earth and. . expresses IS an s 0 e eu sc e . .F h . h ft c. idi th f d c. Planetary Science Letters, 15. 315-319.orsc ungsgememsca lor provi mg e un s lorhis participation in the survey. MARCHIG, V.; ERZINGER, J.; HEINZE, P.M.

(1986): Sediment in the black smoker area of theEast Pacific Rise (18.5°S). Earth and Planetary

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