r/v yokosuka yk18-08 cruise report part i...clinopyroxene-olivine basalt (or andesite), one of which...

R/V Yokosuka

YK18-08

Cruise Report

Part I

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CRUISE REPORT

RV Yokosuka and HOV SHINKAI 6500 Cruise YK18-08

Tairiku Project: Studies of submarine arc volcanism of Doyo Seamount in the Ogasawara arc by using HOV

SHINKAI 6500

Nishinoshima area (50 km north of Nishinoshima Island)

June 25, 2018-July 7, 2018

Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

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Ankaramite, which was unexpectedly obtained but largely exposed during 6K#1519 dive, containing a large amount of coarse clinopyroxene phenocrysts up to 1 cm in diameter.

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INTRODUCTION

Izu-Ogasawara-Mariana (IOM) system of arcs (also known as the Izu-Bonin-Mariana (IBM) arc system) is a typical oceanic arc produced by subduction of the Pacific Plate beneath the Philippine Sea Plate. The Izu-Ogasawara arcs extend from 〜35°N near Tokyo in the north to ~24°N, the northern end of the Mariana arc in the south (Figure 1). FIGURE 1. Doyo Seamount is one of submarine volcanoes in the Izu-Ogasawara arc.

Volcanoes along the southern segment of the Izu-Ogasawara arc are underlain by thin crust (10-20 km). In contrast those along the northern segment are underlain by crust ~35 km thick (Figure 2). Interestingly, andesite magmas dominate eruptive products from the former volcanoes and mostly basaltic lavas erupt from the latter. According to the hypothesis presented by Tamura et al. (2016), rising mantle diapirs stall near the base of the oceanic crust at depths controlled by the thickness of the overlying crust. Where the crust is thin, melting occurs at relatively low pressures

in the mantle wedge producing andesitic magmas. Where the crust is thick, melting pressures are higher and only basaltic magmas tend to be produced.

To examine this hypothesis, we have dived Doyo Seamount to sample primitive magmas from the volcano, which is located about 50 km north of Nishinoshima and is underlain by thinner curst (15 km) compared to Nishinoshima. FIGURE 2. Along-arc variations of water depth and crustal thickness of the Izu-Ogasawara arc.

Doyo Seamount is located approximately 900 km south of Tokyo at 27°41’ N, 140°48’ E in the Ogasawara Arc. The seamount attained an elevation of ~400 m below sea level (mbsl) and its submarine flanks extend to the depth of 3,200 mbsl. The basal dimeter of the volcano is about 30 km. The deeper parts of this large submarine edifice have yet to be explored.

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1. Cruise Information ● Cruise ID: YK18-08 ● Name of vessel: RV Yokosuka and SHINKAI 6500 ○ Title of project: Tairiku Project ● Title of cruise: Tairiku Project: Studies of submarine arc volcanism of Doyo Seamount Volcano in the Ogasawara arc by using HOV SHINKAI 6500 ● Chief Scientist [Affiliation]: Yoshihiko Tamura [JAMSTEC] ● Cruise period: June 25, 2018 to July 7, 2018 ● Ports of departure / call / arrival: Futami Port of Chichijima to Harumi Port of Tokyo ● Research area: Doyo Seamount in the Ogasawara arc ● Research map

FIGURE 3. Doyo Seamount is one of submarine volcanoes in the Ogasawara arc, which is located about 50 km north of Nishinoshima volcano. 2. Research Proposal and Science Party ● Title of proposal Tairiku Project ● Representative of Science Party [Affiliation] Yoshihiko Tamura [JAMSTEC]

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● Science Party (List) [Affiliation, assignment etc.] Tairiku Project Yoshihiko Tamura [JAMSTEC, Lead Proponent] Takashi Miyazaki [JAMSTEC, Sr-Nd-Pb isotope analyses] Osamu Ishizuka [JAMSTEC/GSJ, AIST, Trace element and Ar-Ar age analyses] Tomoki Sato [JAMSTEC, Petrography and XRF analyses] Yasuhiro Hirai [JAMSTEC, Petrography and XRF analyses] Mami Takehara [NIPR, Oxygen isotopes] Eri Sakamoto [NME]

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「よこすか」乗組員名簿 (CREW LIST)

No. 職名 Position 氏名 Name

1 船長 Captain 青木高文 TAKAFUMI AOKI

2 一航士 Chief Officer 三森靖彦 YASUHIKO SAMMORI

3 二航士 2nd Officer 大原登志世 TOSHIYO OHARA

4 三航士 3rd Officer 山口諒 RYO YAMAGUCHI

5 次三航士 Jr.3rd Officer 小澤敢太 KANTA OZAWA

6 機関長 Chief Engineer 野口和徳 KAZUNORI NOGUCHI

7 一機士 1st Engineer 黒瀬航 WATARU KUROSE

8 二機士 2nd Engineer 白潟健一 KENICHI SHIRAKATA

9 三機士 3rd Engineer 貝野潤華 YUNA KAINO

10 電子長 Chief Electronic Op. 小牧洋介 YOSUKE KOMAKI

11 二電士 2nd Electronic Op. 鬼久保竜師 RYUJI ONIKUBO

12 三電士 3rd Electronic Op. 杉本洋平 YOHEI SUGIMOTO

13 甲板長 Boatswain 磯部英男 HIDEO ISOBE

14 甲板手 Quarter Master 村田海人 KAITO MURATA

15 甲板手 Quarter Master 永井大誠 HIROAKI NAGAI

16 甲板手 Quarter Master 川村幸生 KOSEI KAWAMURA

17 甲板員 Sailor 小島真也 SHINYA KOJIMA

18 甲板員 Sailor 村井恭平 KYOHEI MURAI

19 甲板員 Sailor 朝國知希 TOMOKI ASAKUNI

20 甲板員 Sailor 德永拓真 TAKUMA TOKUNAGA

21 操機長 No.1 Oiler 山口由紀広 YUKIHIRO YAMAGUCHI

22 操機手 Oiler 渡辺拓也 TAKUYA WATANABE

23 操機手 Oiler 海藤弘記 HIROKI KAITO

24 操機手 Oiler 佐藤大樹 DAIKI SATO

25 操機手 Oiler 日髙透 TORU HIDAKA

26 機関員 Assistant Oiler 中村健介 KENSUKE NAKAMURA

27 司厨長 Steward 尾上龍也 TATSUNARI ONOUE

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28 司厨手 Steward 福村秀夫 HIDEO FUKUMURA

29 司厨手 Steward 大場寛幸 HIROYUKI OHBA

30 司厨手 Steward 村上勘十郎 KANJURO MURAKAMI

31 司厨員 Steward 阿部黄菜 KINA ABE

32 司厨員 Steward 白崎由樹 YUKI SHIRASAKI

「しんかい６５００」運航チーム(SHINKAI6500 TEAM)

No. 職名 Position 氏名 Name

33 司令 Submersible Op. Manager 櫻井利明 TOSHIAKI SAKURAI

34 副司令 Deputy Submersible Op. Manager 千葉和宏 KAZUHIRO CHIBA

35 一等潜技士 1st Submersible Staff 植木光弘 MITSUHIRO UEKI

36 一等潜技士 1st Submersible Staff 松本恵太 KEITA MATSUMOTO

37 一等潜技士 1st Submersible Staff 齋藤文誉 FUMITAKA SAITO

38 二等潜技士 2nd Submersible Staff 千田要介 YOUSUKE CHIDA

39 二等潜技士 2nd Submersible Staff 鈴木啓吾 KEIGO SUZUKI

40 二等潜技士 2nd Submersible Staff 大西琢磨 TAKUMA ONISHI

41 二等潜技士 2nd Submersible Staff 倉本佳和 YOSHIKAZU KURAMOTO

42 三等潜技士 3rd Submersible Staff 飯島さつき SATSUKI IIJIMA

43 三等潜技士 3rd Submersible Staff 南野直人 NAOTO MINAMINO

6 月 26 日(火) #1518DIVE 潜航者 : 潜水船船長千葉和宏、船長補佐飯島さつき、観察者石塚治（海

洋研究開発機構) 潜航点 : 27°44.2600’ N, 140°43.4000’ E 水深 2,750m：X-Y 原点: 27°43.0000’ N, 140°44.5000’ E 〈備考〉時刻:JST 測位センサ:StarPack、D-GPS 測地系:WGS-84 使用受波

器:#1、#2 6 月 27 日(水) #1519DIVE 潜航者 : 潜水船船長鈴木啓吾、船長補佐千田要介、観察者田村芳彦（海

洋研究開発機構) 潜航点 : 27°41.7000’ N, 140°54.8000’ E 水深 3,020m：X-Y 原点: 27°41.8000’ N, 140°52.8000’ E 時刻:JST 測位センサ:StarPack、D-GPS 測地系:WGS-84 使用受波器:#1、#2

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3. Research/Development Activities Bathymetric surveys R/V YOKOSUKA completed additional bathymetric surveys using a multi narrow beam echo sounder (EM122, Kongsberg Maritime, Inc.) in several areas around the Doyo Seamount and dive sites. These MBES data were merged with existing multibeam data to produce final maps of study area. (Descriptions for research activities, such as:

- Responsible personnel - Purpose, background - Activities (observation, sampling, development) - Methods, instruments - Results - Dive Information (dive number, location, payloads, dive log, sampling, dive track) - Future plans - QC information of data/samples - Lists (samples, observation equipment, deployment & recovery) - Local field map (dive tracks, sampling points, survey lines)

FIGURE 4. New bathymetric map of Doyo Seamount and dive tracks for 6K#1518 and 6K#1519 of SHINKAI 6500. Dive 6K#1518 on June 26, 2018 Observer: Osamu Ishizuka Pilots: Kazuhiro Chiba, Satsuki Iijima Technical information: Location: Northwestern slope of the Doyo Seamount Objective: Observation and rock sampling of primitive magma from satellite cones of the Doyo Seamount

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On bottom: Off bottom:

Time (local) 11:19, June 26, 2018 15:50, June 26, 2018 Latitude: 27°44.3595′ N 27°42.4846′ N Longitude: 140°43.5308′ E 140°44.9684′ E Depth (m): 2744 1857 22 samples collected Purpose:

The main purpose of this dive was to observe and sample rocks from the satellite cones on the NW flank of the Doyo seamount. On the northwestern slope of the volcano, a NW-SE trending chain of small cones were recognized during YK17-14 cruise. Deeper satellite vents are expected to erupt more primitive magma compared to the main summit vents because their magma could bypass the shallow magma chamber where extensive crystal fractionation and accumulation. We aim to recover primitive magmas to well characterize petrological and geochemical character of these magma, and reveal genesis of arc magma where the crust is thin.

This dive aims to observe and collect samples from different levels of a satellite

volcanic chain between 2,750 mbsl and 1,410 mbsl to detect possible along chain variation of erupted magma. The data collected from this dive will provide information about structure of magmatic plumbing of this volcano as well as primary magma of this volcano. Observations:

The dive began at 11:19 (Fig. 1) on a relatively steep slope composed of lava blocks and sand with ripples at 2,744 mbsl. It appears to be partially buried pillow lava flow. Pillow lava surface and radial joints of broken lava blocks are clearly observed. This lava seems to have flowed down from west. Sample R01 and R02 were collected from lava outcrop at around 11:30 (Fig. 2: 2,725mbsl). The collected samples are olivine basalt (or andesite).

At 11:41, beautiful pillow lava flow field appeared at 2,728 mbsl. At 1145, samples (R03, R04, and R05) were recovered from pillow lava surface (Fig. 3). This lava might have flown down from a small volcanic centre at around 2,680 mbsl on the NW-SE trending ridge. Collected samples preserved fresh glassy rind up to 5 mm thick. These samples are clinopyroxene-olivine basalt with some plagioclase phenocrysts.

Occasional lava flows which come down from NW-SE trending ridge were observed (e.g., at 11:48 (2,717 mbsl)), 11:49:55 (2,712 mbsl), 11:52 (2,693 mbsl)), 11:59 (2,652 mbsl)) which suggests that this ridge is an eruption fissure (Fig. 4).

At 12:13 (2,589 mbsl), blocky lava samples were collected in a lava flow which appears to come down from the ridge crest (Fig. 5: R06 and R07). These are clinopyroxene-olivine basalt (or andesite), one of which has 5mm of glassy rind. This lava might have come down from a small edifice at 2,470 mbsl on the NW-SE trending ridge.

Pillow lava flows were frequently observed between 2,585 and 2,531 mbsl (Fig. 6). At 12:40, 2 samples of R08 and R09 were collected from one of such lava flows at 2,531 mbsl (Fig. 7). These samples are olivine basalt (andesite) and possibly from interior of

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the lava (lack in chilled texture). It is difficult to determine the eruption centre of the lava flow, but could be from around 2,350 mbsl on the NW-SE trending ridge.

Lava flows are almost continuously observed, but at round 2,430 mbsl, lava flow was partially covered with sand, and only limited portion of lava surface is exposed on the seafloor. At 13:10 (2,381 mbsl), one sample (R10) was collected from fractured lava outcrop (Fig. 8). This sample is olivine basalt and could have been derived from the vent in the similar area as that for R08 and R09.

SHINKAI now climbed up to the crest of the NW-SE trending ridge. More pillow lavas with brecciated lava blocks or volcanic bombs were observed near the crest (13:22, 2,312 mbsl)). As we climbed up to a small knoll whose summit is at 2,280 mbsl, its steep slope was covered with sandy sediment with ripples (13:29, 2,300 – 2.260 mbsl). Finally, very close to the summit (13:35, 2,254 mbsl), we encountered exposure of possibly spatter. Two subrounded boulder of olivine-plagioclase-clinopyroxene basalt (R11 and R12) were collected (Fig. 9; 13:38, 2,254mbsl) .

After the sampling near the summit, SHINKAI flew to the foot of the next small cone on the NW-SE trending ridge and saw the seafloor at 2,278 mbsl, where blocky (brecciated) and pillow lava blocks were observed (13:47, 2,265 mbsl). There were some large lava boulders with clear radial joints. Possible spatter and lava flow section was observed at 13:49 (2,255 mbsl), and this location is very close to the site of eruption.

At 13:51 (~14:00, 2,243 mbsl), a lava flow with no sediment cover was observed (Fig. 10). Two samples were recovered. R14 was collected directly from lava flow surface with preserved flow texture.

While climbing up to a hump at 2,230 mbsl, there appeared to be an outcrop of a pile of spatter (14:05, 2,232 mbsl). This implies that this hump could be a small volcanic edifice on the NW-SE ridge. This type of outcrop was also observed at 14:07 (2,229 mbsl), which could be spatter rampart.

At 14:17 (2,216 mbsl), pillow lava outcrop forms steep slope with no sediment cover (Fig. 11). At 14:22 (2,202 mbsl), sample R15 and R16 were directly collected from the pillow lava surface. This sample is highly-phyric olivine-clinopyroxene basalt, which is ankaramitic.

Packed pillow lava flows were continuously exposed along the track, forming steep slope. This lava outcrop continued at least up to 2,160m. Then outcrop composed of blocky lava/spatter appeared at 14:33 (2,157 mbsl). Many small branches of lava flow appear to have come down from right hand side (i.e., southern upper slope). At 14:40 (2,126 mbsl), cliff of about 30 - 40m high composed of packed pillow lava was observed (Fig. 12). SHINKAI landed at the uppermost part of the cliff, and collected three samples (R17-19) from pillow lava flow. These samples are moderately-phyric olivine-clinopyroxene basalt. Outcrop of pillow lava continued up to 2,060 mbsl. At 14:55 (2,065mbsl), lava flow appears to have come down from left hand side slope (Fig. 13).

Once we passed over the hump at 2,020 mbsl and started climbing up the slope of a small knoll with a summit depth of 1,870 mbsl, seafloor was covered with sandy sediment with ripples.

Lava flow emerged again at 15:09 (1,993 mbsl), and we collect one sample from this lava flow (Fig. 14, R20). The sample was moderately-phyric olivine-clinopyroxene basalt. Exposure of pillow lava continued up to 1,940 mbsl. At 1,947mbsl, lava flow appears to have come down from right front (from south).

Since the time is running out, we decided to fly over to the next small edifice on the NW-SE trending ridge to do final sampling. We landed near the foot of the slope (1,897 mbsl) of the small knoll with a summit depth of 1,750 mbsl. The observed outcrop appears to be either lava surface or pyroclastic deposits. Highly-vesiculated olivine basalt and olivine-clinopyroxene basalt were collected at 15:40 (R21 and R22) at a water depth of 1,900 m (Fig. 15). Upper slope observed after the final sampling seems to have

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been dominated by volcanic bombs and spatters rather than lava flow, which indicates that the 1,750 mbsl knoll is another volcanic edifice on the NW-SE trending ridge. Dive ended at 15:50 at a water depth of 1,857m. Summary:

Dive #1518 surveyed NW-SE trending volcanic ridge on the NW flank of the Doyo Seamount. This dive successfully recovered 22 volcanic products from possibly 7 small eruption centres located between 2,700 and 1,750 mbsl. Recovered rocks are mostly olivine- or olivine-clinopyroxene basalt (andesite) with few plagioclase phenocrysts, suggesting that the recovered volcanic rocks are relatively primitive, i.e., not strongly differentiated.

There are good exposures of rocks throughout this dive. Most of the outcrop appears to be lava flows with characteristics of pillow lava. Many lava flows seem to have flowed down from the small cones on the NW-SE trending ridge, or ridge crest, which strongly implies that the NW-SE trending ridge is eruption fissure and chain of small satellite volcanoes of the Doyo Seamount. This interpretation is also supported by occurrence of volcanic bomb and spatter. Figures:

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Figure 1 – Submersible track along the dive track. Rock types recovered at each sampling station are also shown.

Figure 2 – Outcrop of lava and sample R01 collected from outcrop (11:26: OUT P6260030. JPG, 11:28: P6260034.JPG).

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Figure 3 – Outcrop of pillow lava and sample R04 (11:43: OUT P6260077.JPG,

11:43: P6260079.JPG).

Figure 4 – Pillow lava observed at 11:55 (OUT P6260115.JPG, P6260118.JPG).

Figure 5– Outcrop of pillow lava and sample R06. (12:09: OUT P6260163.JPG,

12:12: OUT P6260172.JPG)

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Figure 6– Outcrop of pillow lava. (12:19: OUT P6260189.JPG, 12:20: OUT

P6260193.JPG)

Figure 7 – Outcrop of pillow lava and sample R09. (12:36: OUT P6260229.JPG,

12:39)


13:11).

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13:11).

Figure 10 – Outcrop of pillow lava and sample R13 and R14. (13:55: OUT

P6260401.JPG, 13:53).

Figure 11 – Outcrop of pillow lava and sample R15 and R16. (14:21: OUT P6260453.JPG, 14:25, OUT P6260461.JPG).

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Figure 12 – Outcrop of pillow lava and sample R17-19. (14:43: OUT P6260494.JPG, 14:48: OUT P6260504.JPG).

Figure 13 – Outcrop of pillow lava between R17-19 site and R20 site (14:54).

Figure 14 – Outcrop of pillow lava and sample R20. (15:12: OUT P6260552.JPG, , 15:17).

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Figure 15 – Outcrop of pillow lava and sample R21-22. (15:39: OUT P6260612.JPG, 15:39: OUT P6260613.JPG) Dive 6K#1519 on June 27, 2018 Observer: Yoshihiko Tamura Pilots: Keigo Suzuki, Yousuke Chida Technical information: Location: Eastern slope of the Doyo Seamount Objective: Observation and rock sampling of primitive magma from satellite cones and eastern ridge of the Doyo Seamount

On bottom: Off bottom: Time (local) 11:36, June 27, 2018 16:16, June 27, 2018 Latitude: 27°41.4285′ N 27°41.7778′ N Longitude: 140°54.3810′ E 140°52.7837′ E Depth: 3,091 m 2,225 m 21 samples collected Purpose:

The main purpose of this dive was the same with the previous dive #1518. Based on the study using ROV HyperDolphin in the Mariana arc, we found that primitive lavas tend to erupt in the deeper parts of submarine volcanoes at the depth of ~2,000 m (Tamura et al., 2011; Tamura et al., 2014). We dived to the deeper parts of Doyo Seamount to observe and sample primitive magmas. Deeper satellite vents are expected to erupt more primitive magmas compared to the main summit vents because primitive magmas could bypass the shallow magma chambers where crystal fractionation and magma mixing happen. We aim to recover primitive magmas to well characterize petrological and geochemical character of these magmas and source mantle, and to reveal the genesis of andesite magmas and continental crust in the oceanic arc where the crust is thin (Tamura et al., 2016).

There is a small satellite cone about 11 km east of the summit at the depth of ~3,000 m. A ridge extends on the flank of the volcano from the summit in the ENE direction to

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the depth of ~2,400 m. Thus, we tried to sample this satellite cone and the deeper part of the ridge. Observations: At 11:36, we have landed on the seafloor at a depth of 3091 m, which were covered by sand and scattered blocks. Sample R01 and R02 are collected from these blocks (Figure 2). R01 is vesiculated ankaramite, but R02 is plagioclase-clinopyroxene basalt, which has no vesicles. Thus, these rocks are boulders derived from the topographic high. There is a small satellite cone south of this landing point, thus these rocks could be derived from this satellite cone. Figure 3 shows the outcrop where we have sampled R03 and R04 at a depth of 2956 m. These are vesiculated clinopyroxene-plagioclase basalt and olivine-clinopyroxene basalt, respectively, but are not ankaramites. The surfaces of blocks are rather smooth. This outcrop could be a talus of the end of a lava flow, which have flowed down from west to east. R05, which is strongly vesiculated (~30 % vesicles) plagioclase-olivine-clinopyroxene basalt, was recovered from the outcrop of Figure 4 at a depth of 2,935 m. The outcrop could be a talus of the end of lava flow. However, this could be also a part of submarine volcaniclastic cone consisting of strongly vesiculated scoriaceous lava blocks. R06 and R07 had been collected from brecciated lava flow (Figure 5) at a depth of 2,905 m. R06 looked like a part of pillow lava (Figure 6). These blocks are less vesiculated compared to ankaramite lavas. R08 is vesiculated olivine-clinopyroxene basalt (ankaramite) collected at a depth of 2,833 m from a talus, possibly at the end of lava flow (Figure 7). There is a small flat area just south of this site, which could represent the main body of a lava flow. The blocks had rough and rugged surfaces, which could be a particular character of ankaramite. Samples R09 to R13 are phenocryst-poor olivine basalts. Figure 8 shows an outcrop of pillow lava at the depth of 2637 m, where R10 and R11 had been recovered. This is a small E-W ridge derived from the main ENE ridge. However, pillow lavas change into rough and rugged lavas again at a depth of 2466 m (Figure 9), and blocky lava flow at a depth of 2401 m (Figure 10), which consist of ankaramites (R14 and R15, and R16, respectively). We observed a beautiful pillow lava at a depth of 2,342 m (Figure 11) and collected sample R17 directly from the outcrop (Figure 12), which is found not to be ankaramite but olivine-plagioclase-clinopyroxene basalt. At around a depth of 2,227 m, blocky lava flow covered by sand appeared (Figure 13). The surface of the lava is rough and rugged and four samples (R18, R19, R20, and R21) had been recovered from the outcrop. These are all moderately vesiculated (~20 % vesiculation) ankaramites containing 30-40 % of coarse clinopyroxene phenocrysts. Summary: Interestingly, 13 samples out of all 21 samples, which we have recovered during this dive 6K#1519, are highly vesiculated olivine-clinopyroxene basalts containing 20-40 % of very coarse clinopyroxene phenocrysts, which could be called ankaramite. Surfaces of these ankaramite lavas are rough, which are different from apparently smooth surface of basaltic pillow lavas.

Many parts, however, were covered by rippled sand along the track of 6K#1519.

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Lavas are blocky and brecciated. Thus, it is often difficult to distinguish lava flows covered by sand and sand having scattered lava blocks. Outcrops of pillow lavas are rare and I think the reason is that ankaramite magmas are strongly phyric and vesiculated, and thus, they could not make pillow lavas. Ankaramites are strongly vesiculated and their blocks have rough and rugged surface. Most of ankaramite magmas might have had explosive eruptions at the depth of 2,000~3,000 m, which could have resulted some volcaniclastic cones or local brecciated lava flow. Figures:

Figure 1 – Submersible track of the 6K#1519 dive from 3,091mbsl to 2,225 mbsl. Sampled rocks recovered at sampling stations are shown.

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Figure 2 – Seafloor covered by sand and scattered blocks. Sample R01 and R02 had been collected from these boulders.

Figure 3 – R03 and R04 had been collected. The outcrop was covered by sand and the surface of blocks look smooth. This outcrop could be a talus of the end of a lava flow.

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Figure 4 – R05 was collected from this outcrop, which could be a part of volcaniclastic cone or a talus of the end of lava flow.

Figure 5– Pillow breccias (R06 and R07) had been collected from this outcrop.

Apparently, the outcrop looks like a brecciated lava flow.

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Figure 6– A part of pillow lava (R06) collected from the outcrop.

Figure 7– Talus at the end of a lava flow. R08 was collected from this talus.

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Figure 8 – Outcrop of pillow lava. R10 and R11 had been collected from this outcrop.

Figure 9 – Outcrop of lavas having a rough surface. Samples R14 and R15 had been collected from these rough and bumpy lava flows.

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Figure 10 – Blocky lava flow, where R16 had been sampled.

Figure 11 – Outcrop of pillow lava.

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Figure 12 – Outcrop of pillow lava. Sample R17 was collected directly from this

outcrop.

Figure 13 – This is a surface of blocky lava flow. Each block cannot move easily.

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Figure 14 – Outcrop of blocky lava, where R18, R19, R20 and R21 had been

sampled. Analytical and future plans This work has been supported by JAMSTEC and JSPS Kakenhi Grant no. 17H02987 to Y. Tamura. Tamura presented an advent of continents hypothesis and proposed this cruise to examine the hypothesis with the help of other scientists. Preparation for analyses (desalting and pulverization of rock samples), XRF analyses, and EPMA analyses will be conducted at Yokosuka, JAMSTEC by Sato, Hirai and a part-timer (Hirai). The rock powders will be sent to Ishizuka to carry out trace element analyses by using ICP-MS at GSJ/AIST. Based on the trace element analyses, Miyazaki and JSPS part-timer will do leaching and Sr-Nd-Pb (Hf) isotopic analyses of selected samples. Ishizuka will select samples for Ar-Ar age determinations from these two dives and send the samples to Takehara, who will crash these samples by using SELFRAG and send the crashed samples back to Ishizuka. Ishizuka will use the groundmass of these samples and determine the erupting ages of lavas by using Ar-Ar methods. Takehara will measure oxygen isotopes of olivine phenocrysts of lavas collected in the dives by using sensitive high-resolution ion microprobe (SHRIMP-IIe/AMC) at NIPR. Tamura will lead a paper to examine the hypothesis and a new finding of ankaramite at Doyo Seamount. ○ 4. Cruise Log （航海中のイベントを時系列で記載。 Time line description of events during the cruise.） ● 5. Notice on Using (下記、取得データやサンプルについての、ユーザーへの通知事項を付記。Insert the following notice to users regarding the data and samples obtained.)

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This cruise report is a preliminary documentation as of the end of cruise. This report is not necessarily corrected even if there is any inaccurate description (i.e. taxonomic classifications). This report is subject to be revised without notice. Some data on this report may be raw or unprocessed. If you are going to use or refer the data on this report, it is recommended to ask the Chief Scientist for latest status. Users of information on this report are requested to submit Publication Report to JAMSTEC. http://www.godac.jamstec.go.jp/darwin/explain/1/e#report E-mail: [email protected]

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Sam

ple

list o

f 6K#

1518

30

Sam

ple

list o

f 6K#

1519

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Photos of collected rock samples

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Research Vessel YOKOSUKA

R/V Yokosuka in Futami Harbor of Chichijima Island, Japan R/V YOKOSUKA was originally designed to serve as the mother vessel for SHINKAI 6500. Since the construction of an autonomous underwater vehicle (AUV), URASHIMA, YOKOSUKA has been shared by SHINKAI and URASHIMA. It has silent engine, advanced acoustic navigation systems and an underwater telephone for its state of the art operations. There are 5 laboratories on Yokosuka, No.1-No.4 laboratories and No.1 Study room. No.1 Lab. has dry space. The permanent installations are PC and a printer. No.2 Lab. has semi-dry and wet space. There are two freezers (-40 and -80 degrees Celsius), an incubator, a Milli-Q, and a fumigation chamber at dry one, and wet one. No.3 Lab. has dry space with storage. No.4 Lab. has semi-dry and wet space. There are a rock saw and a Milli-Q. No.1 Study room has dry space, there are a gravity meter, a data acquisition system of gravity meter, a 3 axis fluxgate magnet meter and also a proton magnet meter, a work station for data processing, and a A0 size plotter. The general specifications of R/V YOKOSUKA Length overall 105.2 m Beam overall 16.0 m Depth 7.3 m Draft 4.5 m Gross tonnage 4,439 tons Service speed 16knot Main propulsion system Diesel engines 2,206kW x 2 Main propulsion method Controllable pitch propeller x 2 Complement Crew 28 persons Submersible operation staff 8 persons Researchers 16 persons Total 52 persons R/V YOKOSUKA MBES / magnetometers / gravity meter

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YOKOSUKA is equipped with various kinds of underway geophysical equipment, a multi narrow beam echo sounder (EM122, Kongsberg Maritime, Inc.), a gravity meter (Type S-63, LaCoste & Romberg Gravity Meters Inc.), a ship borne 3 axis magnet meter (Type SFG-1212, Tierra Technica Inc.), and a proton magnet meter (Type STC 10, Kawasaki Geological Engineering Co., Ltd.). The specifications of these instruments are listed below. The specifications of EM122 Measurement depth (m) 20 ~ 11,000 Measurement frequency (kHz) 12 Measurement method cross fan beam style Beam numbers 288

Measurement point 432 Pulse lengths 2/5/15msec CW(～2000m)

100msec FM(2000m～) Beam width (deg.) 2 Beam interval (deg.) 2 Swath width (deg.) 150 (Max) Sampling rate (msec.) 0.33 Roll (deg.) ±15 Pitch (deg.) ±10 Yaw (deg.) ±10 The specifications of Gravity meter Measurement range (m Gal) 12,000 Drift 3mGal per month or less Stabilized platform Platform pitch(deg.) ±22 Platform roll(deg.) ±25 Platform period(min.) 4 to 4.5 Beam interval(deg.) 1 Control system Recording rate(Hz) 1 Serial out put RS-232 System performance Resolution (mGal) 0.01 Static repeatability (mGal) 0.05 50,000m Gal horizontal acceleration (mGal) 0.25 100,000m Gal horizontal acceleration (mGal) 0.50 100,000m Gal vertical acceleration (mGal) 0.25 Dimension (cm) 71×56×84 Weight (kg) Meter:86, UPS:30 The specifications of 3 axis magnet meter System ring core fluxgate Number of component directly 3 axes Cable length (m) 50 Sensor dimension (mm) φ280×130H Measurement range (nT) ±100,000 Resolution (nT) 1

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The specifications of Proton magnet meter Measurement range (nT) 3 ~ 7 x 10**4 Resolution (nT) 0.01 Sampling rate 10sec, 20sec, 1min, manual, external Time of applying field(sec.) 3 to 10 Sensor dimension (mm) φ200×1050 Weight (kg) 28.6(in the air), 6.2(in the sea)

Human Operated Vehicle (HOV) SHINKAI 6500

HOV SHINKAI 6500 of the surface of the sea diving to Doyo Seamount

SHINKAI 6500 is Human Operated Vehicle (HOV). The HOV navigation consists of two sub-system, SSBL (Super Short Base Line) and LBL (Long Base Line). INS and DVL data logged in slc format include status of HOV, there are acoustic sonar equipment,

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temperature gauge and CTD sensor. The general specifications of SHINKAI 6500 Length 9.7 m Width 2.7 m Height 4.1 m Weight 27 t Maximum operation depth 6,500 m Speed (Cruising) 2.7 knots Speed (Seafloor Observation) 1.0 knots Positioning SSBL/LBL Forward Looking sonar Frequency 105～120kHz Detection range 6,20,60,200,600,1000m Angle of traverse 360° CTD/DO The general specifications of SeaBird Electronics SBE19/SBE43 Measurement range -5 to + 35 ℃ 0 to 70 mS/cs 0 to 15,000 psia Initial accuracy 0.01 ℃ 0.01 mS/cm 0.015% full scale 0.01 ml/l INS (Inertial Navigation System) Measurement range ±180 ℃ (Φ)、±90 ℃ (θ) Initial accuracy 0.1 ° × 1/COS(Lat) Current Direction / Speed Meter Measurement range (Speed) 0 – 6 knots (Direction) 0 – 360 ° Initial accuracy (Speed) 2cm/sec (0-40 cm/sec)、5% FS(40-300 cm/sec) (Direction) 5°(22.5-300m/sec) Depth meter Type Crystal oscillator Measurement range 0 – 133.8MPa Initial accuracy 0.01 FS Altimeter Frequency 14.829 kHz Measurement range 2 – 1000m ADCP Frequency 300 kHz Measurement range – 128m Temperture gauge Measurement range 0 – 400 ℃ Initial accuracy 0.15 ℃ (0 – 100℃) 0.03 ℃ (100 – 400℃)

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SSBL

CTD/DO

ADCP

Forward Looking Sonar

Thruster

No1.Camera No2.Camera / Still Camera

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Cup of Ramen made of forming polystyrene had shrunk and diminished in size about 60 % by the hydraulic pressure at the water depth of 3,000 m (~300 atmospheric pressure).

Keigo Suzuki and Yousuke Chida, Submersible staffs of SHINKAI 6500 team, working in the vehicle during the dive #1519.

R/V Yokosuka

YK18-08

Cruise Report

Part II

1

R/V Yokosuka “Cruise Report”

YK18-08

Evolution of the Lithosphere–Asthenosphere Boundary: A new and dynamic picture of the solid Earth

Around Minamitorishima Island

Jun.25,2018-Jul.7,2018

Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

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Contents 1. Cruise Information 2. Researchers 3. Observation

3.1. Background 3.2. Cruise Objectives 3.3. Activities

4. Notice of Using

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1. Cruise Information Cruise ID: YK18-08 Name of vessel: R/V Yokosuka Title of cruise: Evolution of the Lithosphere Asthenosphere Boundary: A new and dynamic picture of the solid Earth Chief Scientist [Affiliation]: Yoshihiko Tamura [JAMSTEC] Representative of Science Party [Affiliation]: Shiki Machida [Chiba Institute of Technology] Cruise period: June 25th, 2018 – July 7th, 2018 Ports of departure / arrival: Futami (Chichijima) / Harumi (Tokyo) Research area: Around the Minamitorishima Island Research map

Figure 1-1. Ship track during the cruise YK18-08.

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2. Researchers Chief Scientist Shiki Machida Senior Research Scientist, Chiba Inst. Tech. Chief scientist of the project on “Evolution of the Lithosphere Asthenosphere Boundary: A new and dynamic picture of the solid Earth” Onboard Researchers Scientist Junji Kaneko Researcher, JAMSTEC Scientist Teruaki Ishii Researcher, Shizuoka Univ. Scientist Keishiro Azami JSPS Researcher, the Univ. Tokyo Scientist Tomoya Obase Doctor Student, Tohoku Univ. Scientist Yuzuki Shinji Master Student, Tohoku Univ. Marine Technician Eri Sakamoto Nippon Marine Enterprises, Ltd. Shore-based Researchers Scientist Naoto Hirano Associate Professor, Tohoku Univ. Scientist Masao Nakanishi Professor, Chiba Univ. Scientist Hidenori Kumagai Group Reader, JAMSTEC Scientist Kazutaka Yasukawa Researcher, The University of Tokyo

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3. Observation by Shiki Machida

3.1. Background Petit-spot, new type young volcanoes discovered on the old Pacific plate, is caused by that the

magma exudes where the plate flexes and fractures before subducting [1]. Our recent experimental studies defined that primitive alkali magma forming petit-spot originates from CO2-rich silicate melt in the asthenosphere [2], which is always produced because of the existence of CO2-rich fluid or carbonate (Fig. 3-1) [3, 4]. Furthermore, the formation of melt ponds before eruption at the lithosphere–asthenosphere boundary (LAB) is needed to explain the localized hot geotherm of the petit-spot volcanoes [5], which is proposed on the basis of investigation on peridotite xenoliths. The ponding is caused by the horizontal melt migration against the plate motion beneath the LAB owing to the pressure gradient that is induced by the excess topography of the outer rise, which is the difference in depth between the shallow seafloor at the top of the outer rise and deep normal seafloor [5]. In addition, the position of the eruption of magma in a petit-spot volcanic field temporally migrates opposite to the direction of the movement of the Pacific plate, accompanying gradual change of the erupted lava geochemistry [6]. These observations were explained by a new eruption model [6] that considered a petit-spot volcanic field to correspond to an isolated melt pond at the LAB (Fig. 3-2).

However, the nature of lithosphere–asthenosphere boundary (LAB) is not clarified yet, even though which is critical boundary zone defining structure of the Earth and regulating circulation of the Earth’s interior. We think that detailed geochemical investigation for petit-spot volcanoes will provide key constraints on our understanding of the nature of evolution (i.e., spatiotemporal changing on chemistry) of LAB.

Figure 3-1. A model for the eruption of petit-spot volcanoes modified from Hirano et al. (2006) on the basis of results of Machida et al. (2017).

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Figure 3-2. Schematic cross-sections illustrating a model that explains spatiotemporal variations in petit-spot volcanism on the Cretaceous Pacific Plate (Machida et al. 2015).

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Figure 3-3. Map showing location of survey area during cruise YK18-08. Red square indicates the survey area of this cruise. White square in the survey area indicates the region around dive sites shown in Fig. 3-4. Orange squares indicate the range of the Petit Spot Volcano field (Site A, B, and C) in the Northwest Pacific.

Presence of petit-spot volcanoes around the Minamitorishima island was expected on the basis

of the precise data of bathymetry and backscatter intensity of Multi narrow Beam Echo Sounder (MBES), acquired by the Japan Coast Guard [7]. Then, in 2010, we conducted a research cruise of R/V Yokosuka (YK10-05) to find petit-spot volcanoes in the south of Minamitorishima island (Fig. 3-3). As a result, we had found only one small seamount at approximately 100 km SW of the Minamitorishima island (Fig. 3-4; Hirano et al., in review). The other investigated knolls are not active volcanoes. They are knoll covered by thick ferromanganese crust and large number of ferromanganese nodules (YK10-05 Cruise Report, 2010). We thus concluded that there are quite small number of young petit-spot volcanoes in this region.

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However, recent acoustic investigations for mineral resources in the Japanese Exclusive Economic Zone (EEZ) around the Minamitorishima island provided some critical information suggesting existence of young activity of petit-spot lava. These investigations were conducted by the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) during seven cruises KR13-02 and KR14-02 of R/V Kairei and MR13-E02, MR14-E02, MR15-E01 and MR15-02 of R/V Mirai. Based on results of these cruises, it was defined that the regions showing high acoustic backscatter intensity are widespread especially in southeastern quarter of EEZ around Minamitorishima Island (JAMSTEC Press Release, 26th august, 2016). Especially in the region of SW of the Minamitorishima island, where previously investigated during cruise YK10-05, we observed exposing of acoustically opaque layer on the seafloor using the shipboard sub-bottom profiler (SBP) (Figs. 3-4 and 3-5). Such acoustic feature is different from that of dense ferromanganese nodule field, showing approximately 10 m of acoustically transparent layer (Fig. 3-5). Furthermore, during dives of the submersible Shinkai 6500 during cruise YK16-01 of R/V Yokosuka, an outcrop showing type-configuration of petit-spot lava was found (the dive 6K#1460; Fig. 3-6) and a large number of fresh petit-spot lava samples were collected (the dive 6K#1466; Fig. 3-7).

Therefore, we consider that this region has high potential for many volcanic activities of young petit-spot. Then, it is expected that the distribution of petit spot volcanoes in the Japanese exclusive economic zone (EEZ) around Minamitorishima Island, the composition of magma sources and the eruption age distribution are clarified. Based on these comprehensive investigation, evolution of LAB, a new and dynamic picture of the solid Earth, will be established.

Figure 3-4. Map of detailed topography of survey area during cruise YK18-08. Data were collected sing MBES during the cruises YK10-05. Red circles indicate the site of 6K dive during this cruise. Symbols with alphanumeric annotation indicate dive sites during the previous cruises of R/V Yokosuka (YK10-05 and YK16-01). Colored lines indicate ship track for vessel-equipped SBP during the previous cruises. Along these ship tracks, white color means that acoustically opaque layer is exposed on seafloor.

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Figure 3-5. Comparison of records of the vessel-equipped SBP and features of the seafloor at the place where ferromanganese nodules and sediments are distributed (left) and where lava or manganese crusts are distributed (right). The left profile of SBP is mirror-reversed for easy comparison.

Figure 3-6. Photograph of an outcrop found during the dive of Shinkai 6500 (6K#1460). During this dive, any samples were not collected from this outcrop.

Figure 3-7. Photograph of an outcrop of petit-spot lava observed and sampled during the dive of Shinkai 6500 (6K#1466).

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References [1] Hirano, N. et al. Volcanism in response to plate flexure. Science 313, 1426–1428 (2006). [2] Machida, S., Kogiso, T. & Hirano, N. Petit-spot as definitive evidence for partial melting in the

asthenosphere caused by CO2. Nature Communications 8, ncomms14302 (2017). [3] Hirschmann, M. M. Partial melt in the oceanic low velocity zone. Phys. Earth Planet. Int. 179,

60–71 (2010). [4] Sifré, D. et al. Electrical conductivity during incipient melting in the oceanic low-velocity zone.

Nature 509, 81–85 (2014). [5] Yamamoto, J., Korenaga, J., Hirano, N. & Kagi, H. Melt-rich lithosphere-asthenosphere

boundary inferred from petit-spot volcanoes. Geology 42, 967–970 (2014). [6] Machida, S. et al. Petit-spot geology reveals melts in upper-most asthenosphere dragged by

lithosphere. Earth Planet. Sci. Lett. 426, 267–279 (2015). [7] Oikawa, M. & Morishita, T. Submarine topography in the east sea to the Minami−Tori Shima

Island, Northwest Pacific Ocean. Rep. Hydrograph. Oceanograph. Res. 45, 13-22 (2009) (in Japanese with English abstract).

3.2. Cruise Objectives The objectives of this cruise are (1) to confirm distribution of petit-spot lava especially in the ferromanganese nodule field and on the slope of small seamounts suggested by the previous acoustic investigation, (2) to elucidate the features on structure of lava flow and (3) sampling of lava. The following items will be done in the survey area (Fig. 3-3) situated in the southeast of Minamitorishima island or east of Takuyo-Daino seamount. 1. Observation of lava fields: Detailed megascopic observation and recording of high-resolution

visual image will be done to define morphological features of petit-spot lava on the basis of dive using Shinkai 6500. One of our target is small seamount exhibiting a peculiar shape characteristic of petit-spot volcano (complicated ridge-like topography). The other one is the seafloor showing high backscatter intensity (determined by the vessel-equipped MBES) and exposing acoustically opaque layer (determined by the vessel-equipped SBP).

2. Sampling of lava and nodules with underlying sediments: Sampling of lava, nodules on the seafloor and pelagic sediment below nodules will be done for comprehensive geochemical and geochronological analysis.

3. Geology of lava in the ferromanganese nodule fields: To identify geological features of outcrops of lava in nodule field and determine the underlying high acoustic reflection which is originated probably from lava intrusions, acoustic stratigraphy will be observed in detail using SBP and MBES equipped on Shinkai 6500. Data of the vessel-equipped MBES and SBP also contribute to interpretation on geology of studied area.

4. Magnetics and Gravity: Surface tow and shipboard magnetic survey will be done to estimate age of the seafloor in the survey area on the basis of magnetic lineation. Shipboard gravity survey using shipboard gravitymeter will be carried out to define structure of basement of the survey area. MBES data also will be used during magnetic and gravity analyses. XBT and CTD data also will be used to recalculate seafloor depth.

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3.3. Activities 3.3.1. Cruise Log 2018/06/25 West ward CHICHI-JIMA (27-16.0N, 141-43.8E)

Weather: Fine but cloudy / Wind direction: SE/ Wind force: 3 / Wave scale: 2 /Swell scale: 1 / Visibility: 8 miles 09:55 Scientists board a ship. 10:00 Proceeding to West Ward of NISHINOSHIMA. 10:30 Briefing about ship's life and safety. 11:15 Meeting with SHINKAI6500 Operation team. 15:20 Arrived at West Ward of NISHINOSHIMA. 15:32 Released XBT（27-40.5275N, 140-58.5389E）. 16:04 Start to MBES survey for tommorow dive. 16:27 End to MBES survey. 16:51 Com'sed to MBES survey for tommorow dive. 17:23 End to MBES survey. 17:50 Start to MBES survey. 19:00 Scientist meeting

2018/06/26 surrounding NISHINOSHIMA (27-44.3N, 140-43.7E)

Weather: Fine but cloudy / Wind direction: ESE/ Wind force: 4 / Wave scale: 3 /Swell scale: 2 / Visibility: 8 miles 06:40 End to MBES survey. 09:48 Hoisted up SHINKAI6500 10:03 Started #1518DIVE operation 11:19 Landed on the sea floor (D=2,744m) 15:50 Left the sea bottom (D=1,857m) 16:28 SHINKAI6500 floated 16:59 Recovered SHINKAI6500 & finished the operation. 19:08 Com’ced MBES area survey. 19:55 Scientist meeting

2018/06/27 surrounding NISHINOSHIMA (27-41.6N, 140-54.3E)

Weather: Fine but cloudy / Wind direction: ESE/ Wind force: 3 / Wave scale: 3 /Swell scale: 2 / Visibility: 8 miles 05:58 End to MBES survey. 09:47 Hoisted up SHINKAI6500 10:01 Started #1519DIVE operation 11:36 Landed on the sea floor (D=3,091m) 16:16 Left the sea bottom (D=2,225m) 17:02 SHINKAI6500 floated 17:29 Recovered SHINKAI6500 & finished the operation. 18:17-18:40 Log of eight figure turn. 18:40 Proceeded to next survey area (Off Minamitori) 20:00 Scientist meeting

2018/06/28 East ward of OGASAWARA islands (28-10.4N, 145-33.5E)

Weather: Fine but cloudy / Wind direction: SE/ Wind force: 4 / Wave scale: 3 /Swell scale: 2 / Visibility: 8 miles 08:30 Clean up Lavoratory & Mounting pay load. 13:00 Confirm payload operation 15:00 preparation Lavoratory 18:00 Scientist meeting

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24:00 Adjustment to a time change(+1hour：UTC+10) 2018/06/29 Northwest ward of MINAMITORISHIMA (25-29.6N, 150-37.5E)

Weather: Fine but cloudy / Wind direction: E/ Wind force: 5 / Wave scale: 4 /Swell scale: 3 / Visibility: 8 miles 08:30 SHINKAI 6500 Tour 09:15 Meeting with SHINKAI6500 Operation team. 13:00 Science meeting about tommorow DIVE. 18:00 Scientist meeting

2018/06/30 Off MINAMITORISHIMA (23-31.4N, 155-04.5E)

Weather: Fine but cloudy / Wind direction: ENE/ Wind force: 6 / Wave scale: 5 / Swell scale: 3 / Visibility: 8 miles 05:20 Arrived at research area. 05:30 Released XBT (23-06.3897N, 154-20.0385E) 05:58-06:29 Carried out MBES mapping survey (pre-dive survey) 06:30 Suspended "SHINKAI 6500" submergence survey due to rough sea. 07:01 Com'ced towing to proton magnetometer. 07:19-07:42 Carried out eight figure turn. 09:00 Pay load (SBP) check. Science meeting. 11:00 Released XBT (23-24.7663N, 154-57.3509E) 11:29 Com'ced MBES mapping survey 18:00 Science meeting 19:58 Recoverd Proton magnetometer. 20:44 Com’ced MBES & SBP survey.


Weather: Fine but cloudy / Wind direction: NE/ Wind force: 5 / Wave scale: 4 / Swell scale: 3 / Visibility: 6 miles 09:17 Hoisted up SHINKAI6500 09:31 Started #1520DIVE operation 11:55 Landed on the sea floor (D=5,344m) 15:11 Left the sea bottom (D=5,053m) 16:59 SHINKAI6500 floated 17:33 Recovered SHINKAI6500 & finished the operation. 18:16 Com'ced towing to proton magnetometer. 20:00 Scientist meeting 20:33-22:43 Com'ced MBES & SBP mapping survey. 21:30 #1521DIVE breefing with team 22:45-23:45 Carried out soot blow runnning 23:41 Com'ced MBES & SBP mapping survey.


Weather: Fine but cloudy / Wind direction: ENE/ Wind force: 4 / Wave scale: 3 / Swell scale: 3 / Visibility: 8 miles 03:21 Finished MBES & SBP mapping Survey. 06:37 Finished towing to proton magnetometer. 08:54 Hoisted up SHINKAI6500 09:09 Started #1521DIVE operation 11:43 Landed on the sea floor (D=5,550m) 15:06 Left the sea bottom (D=5,549m) 16:58 SHINKAI6500 floated 17:27 Recovered SHINKAI6500 & finished the operation. 18:10 Com'ced towing to proton magnetometer.

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20:11 Com'ced MBES & SBP mapping survey. 23:58-00:19 Log of eight figure turn.


Weather: Fine but cloudy / Wind direction: NE/ Wind force: 5 / Wave scale: 4 / Swell scale: 3 / Visibility: 6 miles 05:23 Released XBT (23-29.6941N,154-01.0621E) 05:58 Com'ced MBES pre-dive survey. 06:25 Carried out MBES survey. 06:41 Finished towing to proton magnetometer. 08:44 Hoisted up SHINKAI6500 08:58 Started #1521DIVE operation 11:15 Landed on the sea floor (D=5,300m) 15:05 Left the sea bottom (D=5,173m) 16:59 SHINKAI6500 floated 17:30 Recovered SHINKAI6500 & finished the operation. 18:20 Left research area for KEIHIN sec TOKYO.


Weather: Fine but cloudy / Wind direction: NE/ Wind force: 3 / Wave scale: 2 / Swell scale: 2 / Visibility: 8 miles all day Proceeding to HARUMI 08:00 Science meeting 08:30 Removal payload (MBES & SBP) from SHINKAI6500 18:00 Science meeting 24:00 Adjustment to a time change (-1hour：UTC+9)


Weather: Fine but cloudy / Wind direction: SSE/ Wind force: 3 / Wave scale: 2 / Swell scale: 2 / Visibility: 8 miles all day Proceeding to HARUMI 09:00 Scientist Seminor 13:30 Tour of the Engine control room. 18:00 Scientist meeting 19:29-19:49 Log of eight figure turn.

2018/07/06 Southeast ward of Hachijojima (32-31.3N, 140-37.1E)

Weather: Fine but cloudy / Wind direction: SSW/ Wind force: 5 / Wave scale: 3 / Swell scale: 2 / Visibility: 8 miles all day Proceeding to HARUMI 13:00 Clean up at Laboratory 18:00 Scientist meeting

2018/07/07

11:00 Arrived at HARUMI Pier, then completed voy. YK18-08 cruise 3.3.2. 6K Dive YK18-08 cruise operated the three dives 6K#1520 to 6K#1522 in the survey area (Fig. 3-3, and section 3.3.1). The dive logs, related information and corrected samples, are confidential matters. 3.3.3. Multibeam Survey Multi-narrow beam echo sounder (EM122, Kongsberg Maritime, Inc.) surveyed bathymetry and

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acoustic reflectivity of western Pacific, was powerful tool to search the petit-spot lava field during cruise YK18-08. The track lines are shown in Fig. 1-1. The data are confidencial matters. The specifications of EM122

Measurement depth (m) 20 ~ 11,000 Measurement frequency (kHz) 12 Measurement method cross fan beam style Beam numbers 288 Mesurement point 432 Pulse lengths 2/5/15msec CW(～2000m)

100msec FM(2000m～) Beam width (deg.) 2 Beam interval (deg.) 2 Swath width (deg.) 150 (Max) Sampling rate (msec.) 0.33 Roll (deg.) ±15 Pitch (deg.) ±10 Yaw (deg.) ±10

3.3.4 Sub-bottom profiler survey Sub-Bottom Plofiler (SBP; 3300-HM, EdgeTech inc) was used to investigate stratigraphic feature of sedimentary layers of seafloor. The track lines are shown in Fig. 1-1. The data are confidencial matters. The specifications of 3300-HM

Model 4×4 Frequency Range (kHz) 2-16 Pulse type FM Chirp Band width (kHz) 2-16 Pulse length (msec) 5-100 Resolution (cm) 8, (2-12khz) Penetration (m) 80 (Max) Beam width (deg.) 33 (3.5kHz) , 24 (4.5khz) , 20 (6kHz)

3.3.5. Geophysical survey During the YK18-08 cruise, geophysical surveys, whose items included were gravity and geomagnetics, were conducted aboard the R/V Yokosuka around Sites A, B, C, and D (Fig. 3-3). The aim of geophysical surveys was to provide a detailed geophysical characterization of the lithosphere in the western Pacific, which will be used to unravel tectonic evolution and crustal structure. Shipboad gravity anomaly will be used for analysis the crustal structure combined with bathymetry data. The specification of a gravity meter (Type S-63, LaCoste & Romberg Gravity Meters Inc.), a ship borne 3 axis magnet meter (Type SFG-1212, Tierra Technica Inc.), and a proton magnet meter (Type STC 10, Kawasaki Geological Engineering Co., Ltd.) are listed below. The data are confidencial matters. The specifications of Gravity Meter

Measurement range (m Gal) 12,000 Drift 3mGal per month or less

Stabilized platform Platform pitch(deg.) ±22 Platform roll(deg.) ±25 Platform period(min.) 4 to 4.5

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Beam interval(deg.) 1 Control system

Recording rate(Hz) 1 Serial out put RS-232

System performance Resolution (mGal) 0.01 Static repeatability (mGal) 0.05 50,000m Gal horizontal acceleration (mGal) 0.25 100,000m Gal horizontal acceleration (mGal 0.50 100,000m Gal vertical acceleration (mGal) 0.25 Dimension (cm) 71x56x84 Weight (kg) Meter:86, UPS:30

The specifications of Three Axis Magnet Meter

System ring core fluxgate Number of component directly 3 axes Cable length (m) 50 Sensor dimension (mm) φ280Å~130H Measurement range (nT) ±100,000 Resolution (nT) 1

The specifications of Proton Magnet Meter

Measurement range (nT) 3 ~ 7 x 10**4 Resolution (nT) 0.01 Sampling rate 10sec, 20sec, 1min, manual, external Time of applying field(sec.) 3 to 10 Sensor dimension (mm) φ200x1050 Weight (kg) 28.6(in the air), 6.2(in the sea)

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4. Notice on Using Notice on using: Insert the following notice to users regarding the data and samples obtained.

This cruise report is a preliminary documentation as of the end of cruise. This report is not necessarily corrected even if there is any inaccurate description (i.e. taxonomic classifications). This report is subject to be revised without notice. Some data on this report may be raw or unprocessed. If you are going to use or refer the data on this report, it is recommended to ask the Chief Scientist for latest status. Users of information on this report are requested to submit Publication Report to JAMSTEC. http://www.godac.jamstec.go.jp/darwin/explain/1/e#report E-mail: [email protected]

r/v yokosuka yk18-08 cruise report part i...clinopyroxene-olivine basalt (or andesite), one of which...

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