17. volcanic ash at site 584, japan trench117. volcanic ash at site 584, japan trench1 kantaro...

17. VOLCANIC ASH AT SITE 584, JAPAN TRENCH1

Kantaro Fujioka, Ocean Research Institute, University of TokyoJean-Paul Cadet, Département des Sciences de la Terre, Université d'Orleans

andJean-Claude Morin, Laboratoire de Géochimie des Roches Sédimentaires, Université de Paris Sud2

ABSTRACT

Volcanogenic sediments were obtained from Site 584, located on the midslope of the Japan Trench. Occurrences ofvolcanic ash in the diatomaceous mudstones increase within sediments dated 6-3 Ma. The frequency pattern and thesediment accumulation rate obtained at Site 584 are similar to those of Site 440 and to those of Sites 438 and 439, lo-cated on the upper slope basin. Explosive volcanism increased during the Pliocene and late Miocene in relation to theintrusion of Tertiary granites and uplift of the Tohoku Arc (northeastern Japan Arc). Hygromagmaphile element con-centration shows that the glass does not belong to a unique series, and a comparison with Nankai Trough data distin-guishes at least two different evolutionary lines.

INTRODUCTION

During Leg 87B, the middle slope of the JapanTrench was drilled at Site 584, and 940 m of continuoussediments including many volcanic ash layers were ob-tained. Because the site is located on the lee side of thesource area, the northeastern Japan Arc (Tohoku Arc),volcanic ash falls in this area (Fujioka, 1983b). As hasalready reported by Cadet and Fujioka (1980) and Fu-jioka and others (1980), volcanic ash in the upper slopebasin sedimentary sequences at Sites 438 and 439 (JapanTrench) has two distinct Neogene maxima. We expect asimilar pattern of the volcanogenic sediments at Site 584,although the geologic history will be slightly different(von Huene et al., 1980; Shipboard Scientific Party, 1983).

In this report, we present the basic data regarding theexplosive volcanism in the onshore Tohoku Arc throughNeogene times.

LithologySite 584, on the midslope of the Japan Trench fore-

arc, is in a location similar to that of Site 440 (Fig. 1).Pleistocene to middle Miocene diatomaceous mud andmudstones (941 m) were drilled at Hole 584 (ShipboardScientific Party, 1983), which is on multichannel seismicline ORI 78-3 (see fig. 1 in von Huene et al., 1980, andFig. 2). Sediments are divided into four lithologic unitsdepending on the variation in diatom content, abundanceof thin silt beds, and other features (Fig. 3; ShipboardScientific Party, 1983).

Unit 1 is a 4-m thick, Pleistocene, dark olive gray (5Y4/2) diatomaceous mud uncomformably overlying theolive gray diatomaceous mudstone of Unit 2. Unit 3 con-sists of mudstones distinguished from Unit 2 by rela-

Kagami, H., Karig, D. E., Coulbourn, W. X, et al., Init. Repts. DSDP, 87: Wash-ington (U.S. Govt. Printing Office).

2 Addresses: (Fujioka) Ocean Research Institute, University of Tokyo 1-15-1, Minami-dai, Nakano-ku, Tokyo 164, Japan; Jean-Paul Cadet, Département des Sciences de la Terre,Université d'Orléans, 45046 Orleans Cedex, France; Jean-Claude Morin, Laboratoire de Géo-chimie des Roches Sédimentaires, Université de Paris Sud, 91405 Orsay Cedex, France.

tively common, thin fine-sandstone-and-siltstone beds.Strata are inclined seaward and contain healed fractures.Unit 4 is a mudstone with less abundant diatoms andvolcanic ash layers. Thin sandy beds (several mm to 1cm) are frequently encountered in this unit. Bioturba-tion is intense throughout all the cores.

A sedimentation rate curve based on paleomagneticreversals and diatom biostratigraphy (Fig. 4) reveals pe-riods of high accumulation rates from 13 to 11 Ma andfrom 6 to 3 Ma, each followed by times of very low ac-cumulation rates. The latter high sedimentation intervalis identical to the rapid sedimentation period observedat Site 438, drilled in the upper slope basin of JapanTrench.

Volcanic Ash LayersMore than 100 ashy intervals are encountered in the

sedimentary intervals of Site 584 (see end-of-chapter Ap-pendix). Their thicknessess and locations are describedin both Figure 5 and the Appendix. Fujioka (1983b) clas-sified the mode of occurrences of the volcanogenic sedi-ments into three major types by visual core observation.In this core, we encountered all three types of volcano-genic sediments, that is, D, P, and L (D = dispersed insediments; P = pod or pocket; L = layer).

Lithology of the samples is homogeneous throughoutthe core but strongly bioturbated intervals are common(Shipboard Scientific Party, 1983). The thickness of themeasurable volcanic ash layers is similar to and/or slight-ly less than that of ash layers at Site 438 (Fujioka, thisvolume).

Smear-slide data from the volcanic ash layers showsthat ashy intervals contain more than 10% volcanic glassshards (Table 1), and stereographic photographs revealthat these are both pumice and bubble-wall type shards(Plate 1). At Site 584, the ratio of pumice of bubble-walltype glass is high compared to that at Site 436, and lowcompared to that at Site 438, a result of the location ofthis site between Sites 438 and 436 relative to the ashsource (Tohoku Arc).

681

K. FUJIOKA, J.-P. CADET, J.-C. MORIN

42.0°N

41.0c

40.0'

i i

143.0 144.0° 145.0° 146.0°

Figure 1. Location map of Leg 56, 57, and 87B drill sites. Sites 434, 435, and 436 were drilled during Leg 56;Sites 438, 439, 440, and 441 during Leg 57; and Site 584 during Leg 87B. Submarine topography is showntogether with multichannel seismic lines surveyed by JNOC and ORI. Note that only Site 436 is located onthe Pacific Plate, and the others are on the Eurasian or North American Plate.

Deep-sea terrace

Unconformity above Oyashio landmass

Age horizonsPliocene/Miocene

. HoloceneI. Miocene/m. Miocene

•- m. Miocene/e. Miocene L-Top igneous ocean crust J'''^/''

(composite profile JNOC 1 + ORI 78-3)

Figure 2. Situation of drilling sites on the multichannel seismic lines, a composite of profiles JNOC 1 and ORI 78-3 (see Fig. 1 for location). Site 584is located on the midslope of the landward side of the Japan Trench, a setting similar to that of Site 440.

The occurrence pattern of the volcanic ash layers hasa distinct peak around 3-2 Ma. There are no peaks inthe Quaternary and upper Miocene (Figs. 6A and 6B).A frequency diagram was made for L and P types ofvolcanic ash layers. Type D is not taken into account be-

cause it has a distribution concordant with the L and Ptypes at Site 438 (Fujioka, this volume). Age was deter-mined by diatom biostratigraphy and paleomagnetism(Akiba and Niitsuma, this volume), as well as by radio-metric methods (Kaneoka, 1983).

682

VOLCANIC ASHES, JAPAN TRENCH

Holes 584, 584A, 584B

H K140 m 105

438 438Bm 1547.5 m 1558.0 m

400

800

E 1200

ε 1600

2000

2400

2800-

3200 - '><:

435 440 441 434 4363401 m 4507 m 5655 m 5985.8 m 5240 m

s* u. Pliocene

I. Plioceneu. Miocenem. Miocene

MioceneU. Cretaceous

U. Cretaceous

200

400

600

100-

150-

200-

250-

300-

350-

400-

1000

1200

1̂ 1 Volcanic ashE!3 Diatomaceous claystoneE3 Silty claystoneE3 ClaystoneS Siltstone[13 Sandy siltECoalgtt] Volcanic brecciaEH] Calcareous macrofossils1̂ 1 Conglomerate^ 1 Chert

asic igneousE ] Volcanic lapilli[tvl Erratic pebbles (including pumice)E Microfaultsf^7! Veins and healed fractures^ Slump folds: Graded bedding

£§^ Limestonefë&l Calcareous oozeIS31 Breccia

500-

550-

600-

650-

700-

750-

800-

850-

900-

950-

7 B

2a

2b

2c

3a

3b

4b

T. D. = 954.0 m

Figure 3. Lithologic columns of all drilling sites in the Japan Trench region during the IPOD program. Columns H and K are the drill holes by Teise-ki Oil Company on the continental shelf off the northeastern Japan Arc (Tohoku Arc). T. D. = total depth.

683


Age (Ma)

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Figure 4. Sediment accumulation rate curve obtained by magnetobio-stratigraphy of Site 584.

Chemical Composition of Volcanic GlassThe SiO2 content of the volcanic glass ranges from 64

to 80% corresponding to compositions of dacite and rhy-olite, respectively. The A12O3 content varies from 10 to15%, the average is 11%. The FeO/MgO ratio is varia-ble. These chemical compositions plot in a field on aSiO2-(Na2O + K2O) diagram that belongs to the nonal-kalic rock series and that in a FeO-(Na2O + K2O)-MgOdiagram (AMF diagram) exhibits trends similar to thoseof a tholeiitic rock series (Fujioka et al., 1980; Fujioka,this volume).

Neutron Activation Analysis: HygromagmaphileElement Concentration

As a complement to classic analytical methods, weconsidered the hygromagmaphile element content in vol-canic glass shards from Legs 57 and 87B and comparedthe results for the Japan Trench with Nankai Trough data.

METHODSThe neutron activation method used was pure instrumental activa-

tion analysis (without chemical separation), using epithermal neutronirradiation (OSIRIS reactor in Saclay, France, Commissariat de PEn-ergie Atomique Groupe des Sciences de la Terre, Laboratoire PierreSud). Irradiation was performed under Cd vials, followed by severalmeasurements made at different intervals from 8 days to 1 month afterradiation (Chayla et al., 1973). The reference standard used is GNS(De la Roche and Govindaraju, 1976), and the sample standard used isBEN (Govindaraju, 1980; Table 3).

Hygromagmaphile elements (Th, la, La, Ce, Hf, Zr, U, Rb, Cs)defined by Treuil are characterized by a low solid/liquid partition co-efficient. The content of such elements increases in magmatic liquidwith differentiation of the magma. Highly hygromagmaphile elementsin magmatic rock samples representative of liquid keep the same ratiosas in the initial solid form. Consequently, highly hygromagmaphile el-ements issuing from the same homogeneous initial solid are linear-ly correlated, and the straight line issues from the origin (Joron andTreuil, 1977).

Choice and Preparation of SamplesSmear-slide samples were selected for their glass content and their

low feldspar and clay content. All samples were cleaned with ultra-sound to clear the clay from the glass shards. Roughly 120 mg of glasswere crushed and analyzed.

RESULTSApart from iron and sodium whose contents are ex-

pressed in percentages of Fe2O3 and Na2O, other ele-

mental contents are expressed in ppm (Table 2). Analyti-cal accuracy is about 10% for Zr and 5% for other ele-ments. The results for the BEN standard and for thedata used for the reference GNS standard are listed inTable 3.

Some samples were contaminated with diatoms thatcould not be separated from the glass. Consequently,some results are underestimated, but the ratios betweenhygromagmaphile elements are not affected.

Two pairs of elements (Th and U, Th and Rb) arefairly well correlated (Fig. 7). Thus the samples have notundergone any important alteration (Rb and U are af-fected by alteration, Joron et al., 1980; Joron and Treuil,1977). The Th/Ta ratios are between 6 and 31 (Table 2).The values are noticeably higher than those found incalc-alkalic rock series on land, such as samples fromthe Fuji, the Ohmuroyama, and Asama volcanoes where4 < Th/Ta < 12 (Wood et al., 1980).

The analyzed glasses have high La/Tb ratios (13 to37). Contents of transition elements are low whereas thoseof hygromagmaphile elements are high, indicating thatthese glasses issued from a highly differentiated mag-matic liquid.

Th is not correlated with either La, Tb, Hf, or Ta(Fig. 8), rather the ratios spread into different groups,showing no relation between the content of hygromag-maphile elements and the sample age. Because we lackthe most basic series, the rebuilding of the evolution ofthe series is difficult; however, the presence of these dif-ferent groups shows that the analyzed glass does belongto a unique series.

Comparison with Nankai Trough Data (Leg 87A)Quaternary samples from the Nankai Trough show,

as in the Japan Trench, a high Th/Ta ratio (11 to 17, Ta-ble 4), characteristic of a subduction zone. The relationsof Th with Ta and with La are represented in Figure 9,together with the Leg 57 (Sites 438, 439, and 440) andLeg 87 (Site 584) data. Glass coming from the south ofShikoku is more differentiated than that of eastern Hon-shu. They have a higher hygromagmaphile element con-tent; the La/Tb ratio varies from 24 to 45 south of Shi-koku and from 17 to 37 for the samples east of Honshu.This higher differentiation may be linked with the morerecent age of the Nankai Trough samples.

On the other hand, at least two different "evolution-ary lines" can be distinguished in the variation diagrams:(1) a line gathering most of the samples from Leg 57and Site 584 (Leg 87) and (2) a line with a few samplesfrom Leg 57 and Site 584 (Leg 87), and all the samplesfrom Sites 582 and 583 (Leg 87).

DISCUSSIONThe history of the explosive volcanism compiled us-

ing the tephras from Site 584 shows a maximum aroundPliocene and late Miocene times. This result is in goodagreement with the results obtained at Site 438 (Cadetand Fujioka, 1980; Fujioka, 1983b; Fujioka, this vol-ume). The Tohoku Arc is one of the most thoroughlystudied island arcs in the world. The geology and tec-tonic evolution of this arc during the Tertiary have beencompiled and discussed by many authors (Amano, 1983;

684


Kitamura, 1959; Niitsuma, 1978), and the history of thevolcanism of this island arc through the Tertiary has beenequally well studied (Fujioka, 1983a, b; Sugimura et al.,1963; Ozawa, 1963; Horikoshi, 1975). According to thesecompilations, the explosive volcanism in this arc is di-vided into the following periods: an early Miocene, chief-ly andesitic phase of volcanism (Huzioka, 1963; Fujioka,1983a), and a middle Miocene phase of large-scale acidicvolcanism related to the formation of the Kuroko de-posits (Fujioka, 1983a; Kaneoka, 1983). After the lateMiocene, volcanism became bimodal, andesitic in thewestern part of the Tohoku Arc, and simultaneously acidicin the eastern part (Konda, 1974; Konda and Ueda, 1980).In the Pliocene, large-scale acidic volcanism took placeeverywhere in relation to the gradual uplift of the Toho-ku Arc (Huzioka, 1963; Fujioka, 1983a).

CONCLUSIONS

The volcanogenic sediments at Site 584 have a dis-tinct maximum in frequency of volcanic ash from 6 to3 Ma. The peak is in good agreement with the youngerpeak observed at Site 438, suggesting that during Plio-cene times an episode of large-scale acidic volcanism tookplace onshore (Tohoku Arc) in relation to the uplift ofthe Tohoku Arc and to the intrusion of the Tertiary gran-ites accompanied by the vein type ore deposits under thecompressional stress field (Fujioka, 1983a).

The hygromagmaphile element analysis shows two linesof evolution that might be linked to at least two differ-ent sources and that are possibly related to the diversesubduction context of the Japan and Nankai Trench areas.Some of the most differentiated glass sampled east ofHonshu has the same geochemical characteristics as ashfrom south of Shikoku. This glass may have issued frommagma linked to the Philippine Plate subduction andwas than transported northward.

ACKNOWLEDGMENTS

The authors would like to express their sincere thanks to Drs. Ka-zuo Kobayashi and Yujiro Ogawa for their critical reading of the man-uscript. Thanks are also due to Drs. K. Nakamura, T. Furuta, and A.Pouclet and to Mr. K. Koga and Ms. A. M. Dubois for their technicalhelp.

REFERENCES

Amano, K., 1983. Miocene geology of Seki district, Miyagi prefec-ture, northeast Japan—block faulting in Miocene. J. Geol. Soc.Jpn., 89:41-53.

Cadet, J. P., and Fujioka, K., 1980. Neogene volcanic ashes and ex-plosive volcanism: Japan Trench transect, Leg 57, Deep Sea Drill-ing Project. In Scientific Party, Init. Repts. DSDP, 56, 57, Pt. 2:Washington (U.S. Govt. Printing Office), 1027-1041.

Chayla, B., Jafrezic, H. and Joron, J. L., 1973. Analyse par activa-tion dans les neutrons épithermiques. Application à la determina-tion d'éléments en trace dans les roches. C. R. Seances Acad. Sci.,77:273-275.

De la Roche, H., and Govindaraju, K., 1976 . Nouveaux étalons géo-chimiques granite GS.N et feldspath FK.N, Analusis 4(8):347-372.

Fujioka, K., 1983a. Where were the "Kuroko deposits" formed—look-ing for the present day analogy. Min. Geol., Spec. Issue, 11:55-68.

, 1983b. History of the explosive volcanism of the TohokuArc from the core sediment samples of the Japan Trench. J. Vol-canol. Soc. Jpn., 28:41-58.

Fujioka, K., Furuta, T., and Arai, F., 1980. Petrography and geo-chemistry of volcanic glass: Leg 57, Deep Sea Drilling Project. InScientific Party, Init. Repts. DSDP, 56, 57, Pt. 2: Washington (U.S.Govt. Printing Office), 1049-1066.

Govindaraju, K., 1980. Report on three GIT-IWG rock reference sam-ples: Anorthosite from Greenland AN.G.; Basalte d'Essay la CöteBE.N.; Granite de Beauvoir MA.N. Geostandards Newsl., IV(1):49-138.

Horikoshi, E., 1975. Genesis of Kuroko-stage deposits from the tec-tonic point of view. J. Volcanol. Soc. Jpn., 20:341-353.

Huzioka, K., 1963. Geology of the Green Tuff region in Japan. Min.Geol., 13:358-375.

Joron, J.-L., Bollinger, C , Quisefit, J. P., Bougault, H., and Treuil,M., 1980. Trace elements in Cretaceous basalts at 25°N in the At-lantic Ocean: alteration, Mantel composition, and magmatic pro-cesses. In Donnelly, J., Francheteau, J.,-Bryan, W., Robinson, P.,Flower, M., Salisbury, M., et al., Init. Repts. DSDP, 51, 52, 53,Pt. 2: Washington (U.S. Govt. Printing Office), 1087-1098.

Joron, J.-L., and Treuil, M., 1977. Utilisation des propriétés des (ele-ments fortement hygromagmaphiles pour 1'étude de la composi-tion chimique et de 1'hétérogénéité du manteau. Bull. Soc. Geol.Fr., 6(XIX): 1197-1205.

Kaneoka, I., 1983. On the radiometric ages of volcanic rocks from thenorthern part of the Honshu Island. Min. Geol., Spec. Issue, 11:69-78.

Kitamura, N., 1959. Tertiary orogenesis in northern Honshu, Japan.Sci. Rep., Tohoku Univ., Ser. 3, 49:1-98.

Konda, T., 1974. Bimodal volcanism in the northeast Japan arc. J.Geol. Soc. Jpn., 80:81-89.

Konda, T., and Ueda, Y., 1980. K-Ar age of the Tertiary volcanic rocksin the Tohoku area, Japan. J. Jpn. Assoc. Mineral. Petrol. Econ.Geol., Spec. Issue, 2:343-346.

Niitsuma, N., 1978. Magnetic stratigraphy of the Japanese Neogeneand the development of the island arcs of Japan. J. Phys. Earth,26(suppl.):S367-S378.

Ozawa, A., 1963. Neogene orogenesis, igneous activity and mineral-ization in the central part of northeast Honshu. (1) On the Neo-gene igneous activity. J. Jpn. Assoc. Mineral. Petrol. Econ. Geol.,50:167-184.

Shipboard Scientific Party, 1983. Leg 87 drills off Honshu and SW Ja-pan. Geotimes, 28(1):15-18.

Sugimura, A., Matsuda, T, Chinzei, K., and Nakamura, K., 1963.Quantitative distribution of late Cenozoic volcanic materials in Ja-pan. Bull. Volcanol., 26:125-140.

von Huene, R., Langseth, M., Nasu, N., and Okada, H., 1980. Sum-mary, Japan Trench transect. In Scientific Party, Init. Repts. DSDP,56, 57, Pt. 1.: Washington (U.S. Govt. Printing Office), 473-488.

Wood, D. A., Joron, J.-L., Marsh, N. G., Tarney, J., and Treuil, M.,1980. Major and trace-element variations in basalts from theNorth Philippine Sea drilled during Deep Sea Drilling Project Leg58: a comparative study of back-arc-basin basalts with lava seriesfrom Japan and mid-ocean ridges. In Klein, G. deV., Kobayashi,K., et al., Init. Repts. DSDP, 58: Washington (U.S. Govt. PrintingOffice), 873-894.

Date of Initial Receipt: 11 July 1984Date of Acceptance: 5 March 1985

685

Φk .

O

o

>ou0)

Volcanic glass shards

5 10 15 20 25

Number ofash layers/

core

Feldspar

30 0

Quartz + feldspar

10 0.0 0.5 1.0 0

450

Thickness of ash layers (cm)

6 8 10 12 14 16

αΦ

T3

o

500-

550-

600-i

650-

700-

750-

800-

850-

900-

QRΠ -

50 1 =o=z7z-z:z-

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JLL

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7778

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Figure 5. Diagram for the contents of volcanic glass shards, number of ashy beds, quartz and feldspar ratios, and the thickness of the volcanic ash layers.

CO

oo

Table 1. Composition of volcanic ash layers, smear-slide data, Site 584.

Sample (Hole 584)

4-1 4-1 4-1Component

7-2103

8-2 8-2 9-1 9-2 10-2118

11-196

12-328

12-341

12-3128

12-514

13-2104

13-3100

15-3110

16-2130

17-340

17,CC7

19-137

20-295

20-634

21-316

22-3128

23-6125

24-419

24-449

26-1139

27-2 28-527 102

>σaClay

QuartzFeldsparMicaHeavy mineralsClayLithic fragmentsVolcanic ashPalagoniteGlauconitePyriteCarbonateForaminifersNannofossilsDiatomsRadiolariansSpongePlantOthers

2335

5

10

35

3

12

102512785

15

8

15

5

45158

202812

39 40 45 40

2087

tr.12

58

9

401513

23

30tr.

5

301216

18

36

1

4

35108

20

40

3

3075

tr.28

28

14

5026

432

221

31

3285

28

36

41

3043

151

51tr.

3

10129

43

6tr.

1047

1554

tr.

12

2033

20

2584

23

251214

2210

Table 1. (Continued).

Component

Sand

SiltClayQuartzFeldsparMicaHeavy minerals

ClayLithic fragmentsVolcanic ashPalagoniteGlauconitePyrite

CarbonateForaminifersNannofossilsDiatoms

RadiolariansSpongePlantOthers

34-4

72

5851065

2

5

77

4

1

34-412

3535301510

14

20

4

3025

34-622

1030601510

215

303

2

15tr.

8

35-125

580151510

1

15

501

2

1

5

1

35-256

3510551110

22

55

10

2

36-162

2555201510

211

15

1

5

3

1

13

7

36-230

155233

88

18

32

55

19

5

37-418

338591215

10

46

64

5

2

38-141

2570

544

5

76

134

3

39-29

10751554

15

57

21

10

6

40-145

45451065

18

741

14

43-128

26038

66

28

411

52

7

4

49-312

42352322

5

210

41

12

44

50-193

42322612152

18

50

3

51-2138

828

101520

2

105

30

5

10

3

Sample (Hole 584)

54-181

354025128

1186

451142

2

55-3138

304525108

tr.186

321

1

31

15tr.

3

2

55-5120

4545101012

2

108

422

10

1

3

56-140

1080

1064

10

71

31

tr.2

2

1

62-179

6215

238

10

27

52

6

12

3

62-360

90555

37

80

4

1

62-375

30

7015

537

15

3

15

10

71-1125

107020

34

1

85

741

3

!

tr.

78-222

5515

301520

10

425

5

12

80-1131

7015

1512

23

49

7

6

3

83-250

4555

1014

1

262

11

88-1140

354520

515

61tr.

3

12

3

1

89-3147

1535

50127

47

16

32

10

1

2

(pumice)

90-1102

2050

30108

1

27

36234

6

3

91-119

205030

75

1

28

17

3

1018

8

3

95-120

1238

5074

48

151

tr.

101

9

3

2(plant)

96-243

2050

3072

101

732

1tr.

1

3

Sample(Hole584A)

2-262

74350

63

tr.

301

46

tr.

42

1

5tr.

2

2-264

1080

1053

7

77

tr.

41

2tr.

1

Note: Sample numbers are expressed in Core-Section (depth in section in cm). Upper three rows show the volume percentages of the grain size of the materials in the volcanic ash layers, tr. = trace.


Table 2. Instrumental neutron activation analysis of samples from Leg 87 (Site 584) and Leg 57 (Sites 438-440).

Sample

Leg 57

438A-2-5, 20440B-3-1, 32440B-34-2, 27438A-24-1, 98438A-59-3, 67438B-4-1, 77439-8-2, 124439-11-3,71

Leg 87

584-5-1, 126-128584-7-1, 134-135584-9-1, 67-69584-17.CC584-27-2, 27-28584-28-4, 14-16584-34-3, 72-74584-36-5, 83-85584-40-4, 127-129584-83-2, 48-50

Note: Na2O and Fe2(

Numberin Figs.7 and 8

12345678

123456789

10

) 3 in wt.Vo,

Age

PleistocenePleistoceneupper Pliocenelower Plioceneupper Miocene

middle Miocene

lower Pliocene

upper Mioceneupper Miocene

remainder in ppm;

Fe2O3

2.122.312.022.672.743.286.832.84

2.103.973.152.932.283.761.892.22.23.54

Fe2O3 =

Na2O

3.93.83.64.23.32.82.73.2

3.93.75.33.23.63.25.43.93.85.2

Sc

7.78.79.29.89.29.6

13.89

6.812.613.78.08.99.28.05.26.8

11.6

total Fe as Fe2O3

Co

2.83.71.151.2

20.28.54.2

1.46.92.54.22.63.81.62.35.23.2

Ni

71127

135022

6

5.141.1

1.714.713.422.4

5.820.331.312.3

Rb

6742313960425352

77804525434834816647

Zr

165148133158135137153193

11012312184

1641271298493

128

Sb

0.720.450.870.912.202.620.910.83

0.570.491.911.900.591.390.370.580.670.70

Cs

3.51.81.11.93.12.73.33.2

4.14.64.82.21.83.11.53.93.72.4

Ba

6924794343843538465544608

5554859631310428481467841955577

La

15.016.013.115.715.912.718.218.1

17.218.89.67.8

18.815.214.118.917.015.5

Eu

0.850.951.250.980.680.701.290.96

0.860.961.290.611.391.220.980.500.661.36

Tb

0.530.770.840.980.760.340.790.74

0.660.640.730.530.810.760.880.760.540.70

Hf

4.54.44.24.84.43.44.14.9

3.93.93.62.84.73.74.43.33.13.9

Ta

0.250.450.480.430.560.450.730.59

0.440.670.290.220.460.370.300.790.560.48

Th

7.74.83.34.45.83.44.74.9

7.66.83.22.74.14.63.88.98.35.3

U

2.51.51.12.41.41.31.32.0

2.81.91.31.51.51.51.22.82.71.6

Th/Ta

31117

10107.56.58

171011129

1213111511

La/Tb

2821163721162324

26161315232016253222

Table 3. Trace element data (ppm) for international rock standards used for instrumental neutron activation analysis.

Standards

GSN

BEN (Leg 57)

BEN (Leg 87)

BEN

Fe 2 O 3

3.55

12.26

11.65

12.93

Na 2 O

3.77

3.3

4.2

3.6

Sc

7.3

24.5

24

25.5

Co

65

62

57

62

Ni

34

267

254

293

Rb

180

42

42

47

Zr

250

356

277

333

Sb

0.69

0.32

0.27

0.24

Ca

5.43

0.63

0.63

0.67

Ba

1380

982

938

1019

La

70

76.2

74

80.7

Eu

0.69

3.9

3.74

3.83

Tb

0.54

1.17

1.04

1.15

Hf

6.5

5.8

5.3

5.9

Ta

2.81

6.6

6.2

6.8

Th

40.8

9.8

9.8

10.5

U

7.74

2.17

2.3

2.46

Note: Reference concentrations in GSN. Concentrations obtained in BEN using GSN reference concentrations.

Table 4. Instrumental neutron activation analysis of samples from Leg 87, Sites 582 and 583.

Core-Section(interval in cm)

583A-1-3, 20-21

583A-8-3, 71-73583A-8-3, 88-89582B-18-6, 22-23582B-19-2, 70-72582B-58-4, 27-28

Numberin Fig. 9

123456

Fe2O3

1.77

3.803.891.502.531.75

Na 2 O

3.7

4.53.83.94.44

Sc

6.9

12126.3

11.35.2

Co

2.14.96.21.82.22.7

Ni

37.718.92.9

5.36.8

Rb

11913695898682

Zr

144283232159222126

Sb

0.410.960.430.700.320.67

Cs

7.67.74.94.23.85.1

Ba

519706458452421410

La

23.93024.316.322.614.4

Eu

0.61.51.20.5

1.30.5

Tb

0.530.850.860.64

0.940.34

Hf

4.4

76.25.2

6.14.9

Ta

0.79

1.230.850.50

0.800.48

Th

11.4

13.89.78.5

8.86.8

U

2.63

3.992.342.372.181.90

Th/Ta

14.5111117

1114

La/Tb

45

3528

25.52442

Note: Na 2 O and Fe2C>3 in wt.%, remainder in ppm; Fe2C>3 = total Fe as Fe 2 θ3

689


16

Figure 7. A. U versus Th. B. Rb versus Th. Leg 87, Site 584; • Leg57, Sites 438, 439, and 440. See Table 2 for correlation of thesesample numbers with DSDP designations.

900-

950

Figure 6. A. Frequency of volcanic ash layers versus sub-bottom depthat Site 584. B. Number of volcanic ash layers versus age of Site 584sediments. Note the distinct peak from 6 to 3 Ma indicating thatexplosive volcanism increases in the source area (northeastern Ja-pan Arc) during Pliocene and late Miocene times.

690


1.0

0.5

0

_ B

-/ 4

33**

4

7* 5

6

/s

I

.-.2

8

1

5

•10* 2

/i

•-•

1

1•

9* y

IOO

-

5Th (ppm)

10

10 5Th (ppm)

Figure 8. A. La versus Th. B. Tb versus Th. C. Hf versus Th. D. Ta versus Th. All symbols are as in Figure 7. Dashed lines represent lower limits ofthe group.

1.5

1.0

0.5

0

A

' "̂I ^^^ •

I

35

• 4 ^

1

-

(ppm

)

30

20

10

n

B

-

/

* •

i

•

* //

5

4 *

i

3

i

1

2

-

Th (ppm)10

Th (ppm)10

Figure 9. A. Ta versus Th. B. La versus Th. Δ Leg 87, Sites 582 and 583; Leg 87, Site 584; • Leg 57, Sites 438, 439, and 440. Dashed lines representlower limits of the group. See Tkble 4 for correlation of these sample numbers with DSDP sample designations.

691


APPENDIXList of Observed Volcanic Ash, Site 584


Hole 584

1-1, 143-1441-2, 12-151-2, 20-241-2, 37-391-2, 100-1051-3, 17-19

1-4, 631-6, 552-1, 412-4,753-1, 40-42.24-1, 0-24-3, 974-4, 644-4, 113-1184-5, 34-6, 20-234-6, 62-645-1, 127-1285-2, 16-185-2, 55-605-2, 1405-2, 1505-3, 157-1, 15-15.37-2, 101-1058-2, 55-598-2, 60-629-1, 60-689-2, 43-4710-2, 75-7610-2, 118-12011-1,95-96.512-3, 27-3012-3, 39-4212-5, 17.5-1912-6, 95-9613-2, 98.5-10313-3, 100-10415-3, 125-12815-4, 7-816-2, 122-13317-3, 26-4617-3, 10018-1, 3919-1,65-6819-1, 88-9119-2, 135-13720-2, 91-9420-6, 3221-3, 16-17.522-3, 74-8722-3, 127-13223-6, 121-12723-6, 113-11524-4, 17-2324-4, 10026-1, 140-14226-2, 35-37.526-4, 5026-4, 124-13026-5, 116-11927-2, 27-3028-1, 131-13228-4, 1628-5, 10229-3, 8729-4, 99-10029-4, 103-10634-4, 72-7534-4, 7734-5, 141

Thicknessof ash layer

(mm)

830

12

< l2-3

7

2020

750

1020

20?

74040208040

20104

302-6

10

83010

110200

52

3030

308

151305060

601

2025

60

3010

10< l30

Composition (•%)(sand/silt/clay)

25/52/23

50/40/10

45/25/30

55/30/15

15/40/4540/40/20

Color(Munsell

chart)

25YN7

2.5Y 6/12.5Y 4/1

25 Y 6/12.5Y 5/15Y5/3

2.5Y 4/12.5Y 4/12.5Y 5/12.5Y 5/1

2.5Y 5/1

5Y7/32.5Y 3/12.5Y 5/1

N6-N7N6N7N7N5

5Y7/3

5Y 5/1

N6

25Y 6/15Y4/15Y5/15Y3/15Y4/3

5Y 6/1-6/25Y5/3

N7

5Y7/3N7

5Y6/1

5Y6/15Y 6/2

5Y5/2

5Y6/1

rçiuapαi

Feldspar

+ quartz

0.125

0.22

0.24

0.32

0.3

Vol.% ofheavy

minerals

10

8

7

8

37

Remarks

L. Bottom sandy, top silty grading

Very thin white pumice layerWhiteDeformed siltyP. silty

Coarse sandy Hb. Cpx. Kf.P. very fine

L. Q. Mt. LithicP. siltyP.P.

L. graded Hb. Cpx.P. sandy gray pod

P. dark gray podP. sandy grayThin and fineL.L. Hb. Cpx. Mt.L. siltyL. gray siltyL. yellowish gray irregularPumice 10 × 5 mm

L. irregular grayL.L. irregularly bioturbatedL. irregular grayL.L.Discontinuous burrowL. upper contact not well definedP.L.

white

sand size ash(?)whitegray sandyfinelight-coloredburrow-filled very fine silty ashpale yellow very fine (silty)very fine silty, lower boundary irregularthinly mottled burrow fillmuddy medium graythingrading graylight olive grayash-filled burrowfine muddy ashash-filled burrowsandygray siltygray siltygrayburrow-filled silty ashvery fine silty ashash-filled burrowwhite

sandy

692

Appendix. (Continued).



Thicknessof ash layer

(mm)

72030

10402040

3010104040

63026115020

2-3

1010

100101045

2204030301020301010102

5010

1301015

501030101030

2<IO

25155

<IO105

<IO2030

8

20205040

3812

Composition (%)(sand/silt/clay)

Color(Munsell

chart)

2.5Y 4/12.5Y 7/12.5Y 4/1

N7N6N5N6

N6/26/2

N6/2N6/1N6/1N5/1

5Y5/2N7N7N7

5Y7/2N6N6

N7

N4N8N7

N6

N5/2

N6-N7

N5N6-7

N6-N7

N5N6N8

N6

N6

5GY 3/2

N7

N6-N7N8

reiusµ<uFeldspar+ quartz

Vol.% ofheavy

minerals Remarks

L. double layer

L.L. white fine siltyP. siltyP. siltyL. siltyL.L.L. siltyP.P.L. siltyGray green diffuse ashL. grayL. whiteL. fineL. very fineL. siltyP. thin laminated siltyL. light gray very fineP. gray siltyL. grayP. gray sandyL. sandyL. gray sandyL. siltyP. siltyL. white siltyL. gray siltyL. sandyL. gray sandyL. gray fine sandyL. sandy inclinedL. gray siltyL. gray siltyL. upper contact indistinct light grayL.L. grayL. volcanic sandL.L.L.P. burrow fillingL. dark grayP.L. inclined, fine grayL. siltyL. sandy silty whiteL. offset of heated fractureP. sandyP. sandyP.L. gray sandyP. ash-filled burrowsP.L.P.L. burrowed siltyL. siltyL. sandy black (?)P.P.P.L. gray sandyP. sandyL. siltyP. burrow filledL. siltyL. sandyL. sandyL. silty dark green lamina

L. siltyL. silty

Hole 584 (Cont.)

34-6, 20-25

34-6, 41-4235-1, 26.5-28.535-1, 33-3635-1, 5035-2, 57-5835-3, 97-10135-3, 101-10336-2, 28-3236-2, 100-10136-2, 134-13736-4, 26-2736-5, 20-2136-5, 80-8437-2, 123-12437-3, 42-42.537-4, 16-1937-4, 111-11437-5, 69.5-70.637-5, 89-9438-1, 41-4338-1, 7638-4, 41-4338-5, 25-538-5, 30-3138-5, 59-6939-2, 10-1139-2, 38-4039.CC, 20-24.540-4,27

40-4, 129.5-131.540-1, 43-4742-1, 58-6143-1, 26-2943-1, 7548-4, 45-4749-3, 12-1649-3, 5849-4, 79-8650-1, 92-9352-2, 6452-3, 77-8352-2, 7753-2, 32-4553-3, 65-7054-1, 80-8554-3, 145-15054-5, 118-12454-5, 13054-6, 47-5054-6, 99-10054-6, 112-11355-5, 117-12056-2, 75-9056-4, 100-10560-1, 12462-1, 74-7862-3, 55-6071-1, 125-13378-2, 2279-3, 15-2080-1, 126-13181-2, 11883-2, 50-5383-5, 0-388-1, 138-14388-2, 13090-1, 102-10491-1, 16-1995-1, 20-2596-2, 41-45

Hole 584A

2-2, 61-682-2, 64-66

Note: Column F/(F + Q) shows the ratio between quartz and feldspar determined by X-ray diffraction (Matsumoto, this volume). L. = layer, P.pod or pocket, Hb. = Hornblende, Cpx. = Clinopyroxene, Kf. = K-feldspar, M. = Magnetite.

693


Plate 1. 1. Stereographic photograph of some volcanic ash layers (rich in bubble-wall type shards) obtained from Site 584; scale is about 5 mmfrom top to bottom of the photo. 2. Stereographic photograph of the volcanic ash layer (rich in pumice-type shards) obtained from Site 584;scale same as in previous figure.

694

17. volcanic ash at site 584, japan trench117. volcanic ash at site 584, japan trench1 kantaro...

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