R/V KAIREI Cruise Report KR13-14

Transcription

1 R/V KAIREI Cruise Report KR13-14 R/V KAIREI + ROV KAIKO7000II Deep Sea Research Structure and dynamics of subduction channels in intraoceanic subduction zones (Ohmachi Seamount, Izu-Bonin arc) August 30, 2013 September 12, 2013 Yokosuka Naha Japan Agency for Marine-Earth Science and Technology (JAMSTEC)

2 Contents 1. Cruise Information 2. Backgrounds and objectives 3. Operation and preliminary results 3.1 Side scan sonar imaging 3.2 Dive report (7K#609 and7k #610) 3.3 Dredge 3.4 MBES 4. Summary 5. Acknowledgements 6. Notice on using

3 1. Cruise information (1) Name of vessel & Cruise ID R/V KAIREI KR13-14 (2) Title of the cruise 2013 Deep Sea Research: R/V KAIREI / KAIKO 7000II: Ohmachi Seamount, Izu-Ogasawara (Bonin) arc. (3) Proposal number and scientific title S13-36 Structure and dynamics of subduction channels in intraoceanic arcs. (4) Period of the cruise From August 30 to September 12, 2013 (5) Port calls Departure: Yokosuka (August 30, 2013) Arrival: Naha (September 12, 2013) (6) Research area Ohmachi Seamount ( m bsl) 28º º30.0 N, E E (7) Researchers [R/V KAIREI Crew] Captain Chief Officer 2nd Officer 3rd Officer Chief Engineer 1st Engineer Jr. 1st Engineer 2nd Engineer 3rd Engineer Chief Electronics Operator 2nd Electronics Operator 3rd Electronics Operator Boat Swain Able Seaman Able Seaman Able Seaman Able Seaman Sailor YOSHIYUKI NAKAMURA HIROYUKI KATO TOSHIYO OHARA SATORU YOSHIDA KIYONORI KAJINISHI KENZO KATO KOJI FUNAE RYOZO MIKAMI NAOOMI UEMURA HIROYASU SAITAKE YOSHIKAZU KURAMOTO TAKAYUKI MABARA YASUYOSHI KYUKI SHUICHI YAMAMOTO HATSUO ODA YUKITO ISHII SAIKAN HIRAI SHUN MIURA

4 Sailor Sailor No.1 Oiler Oiler Assistant Oiler Assistant Oiler Assistant Oiler Assistant Oiler Chief Steward Steward Steward Steward Steward FUMIAKI OMACHI TOSHIYA SAGA JUNJI MORI MASANORI UEDA DAIKI SATO RYO MATSUUCHI SYOTA SHIMOHATA ATSUMU HARA YUKIO TACHIKI YOSHINOBU HASATANI TATSUNARI ONOUE SEIJI HONDA RYU KUBOTA [KAIKO 7000II operating team] Operation Manager 1st ROV Operator 2nd ROV Operator 2nd ROV Operator 2nd ROV Operator 2nd ROV Operator 2nd ROV Operator 3rd ROV Operator 3rd ROV Operator ATSUMORI MIURA HOMARE WAKAMATSU KIYOSHI TAKISHITA TETSUYA ISHITSUKA SHIGERU KIKUYA SEIJI SHIGETAKE YUDAI SAKAKIBARA TAKUMA GOTO YOICHI YASUE [Onboard scientific team] Chief Scientist HAYATO UEDA* Hirosaki University Co-chief Scientist TADASHI USUKI Academia Sinica, Taiwan Scientist MASAKO USUKI National Taiwan University Scientist YUKA NISHIKAWA National Taiwan University Scientist TAKECHIKA KASAI Hirosaki University Scientist ASAMI SAITO Hirosaki University Scientist NATSUMI IIZUKA Hirosaki University Marine Technician HISAORI IWAMOT Nippon Marine Enterprise, Ltd. Marine Technician YUKI MIYAJIMA Marine Works Japan, Ltd. Marine Technician YHEI TAKETOMO Marine Works Japan, Ltd. Marine Technician TETSUHARU IINO Marine Works Japan, Ltd. Marine Technician MASARU YASUNAGA Marine Works Japan, Ltd. * Representative of the scientific theme. (8) List of scientific operations * Imaging sea-borrom features by KAIKO Launcher side-scan sonar (1 dive) * Observation and sampling of rock exposures by the KAIKO vehicle (2 dives)

5 * Dredging rock samples (7 times towing) * Bathymetry mapping using Multi-beam echo sounder (MBES). (9) Extra apparatus * Top Clinometer (payloaded by KAIKO vehicle) * Dredgers (cylinder and box types). Fig.1 Dimension of the top clinometer. Fig.2 Apparatus of dredge systems (left: cylinder type; right: box type).

6 (10) Cruise log Table 1. KR13-14 cruise log Date Local Time Event Position/Weather/ Sea condition 30-Aug-13 08:00 Scientists onboard. 8/3012:00 (UTC+9h) 09:00 Departure from Sumitomo Heavy Indus., Yokosuka. 10:00-10:40 Lecture for shipboard life and safety. 10:45-11:05 KAIKO briefing. 11:08-11:15 Scientists meeting N, E SW-7 (near gale) 4 (sea moderate) Visibly: 5' 31-Aug-13 15:00 Arrived at the research area. 8/31 12:00 (UTC+9h) N, E 15:20 Released XBT. 16:14 Deployed transponder B. WSW-3 (gentle breeze) 16:36 Deployed transponder A. 2 (sea smooth) 2 (Low swell long) 16:58 Deployed transponder C. 17:48-18:55 LBL transponder calibration. 01-Sep-13 07:44 Launching KAIKO (KAIKO#608Dive). 9/1 12:00 (UTC+9h) N, E 09:50 KAIKO started SSS survey. 14:00 KAIKO finished SSS survey. East-1 (light air) 15:55 KAIKO came up to the surface. 1 (calm) 2 (Low swell long) 18:30-18:50 Scientists meeting. 18:46- Began MBES survey. 02-Sep-13-03:20 Stopped MBES survey. 9/2 12:00 (UTC+9h) N, E 04:46-04:56 Dive point MBES survey. 08:49 Launching KAIKO (KAIKO#609Dive). East-5 (fresh breeze) 11:10 KAIKO landing (3,372m). 3 (sea slight) 14:37 KAIKO left the bottom (3,345m). 16:46 KAIKO came up to the surface. 19:17- Began MBES survey. 20:00-20:10 Scientists meeting. 03-Sep-13-00:18 Stopped MBES survey. 9/3 12:00 (UTC+9h) N, E 08:39 Launching KAIKO (KAIKO#610Dive). 11:05 KAIKO landing (3,361m). ESE-5 (fresh breeze) 14:04 KAIKO left the bottom (3,335m). 3 (sea slight) 16:11 KAIKO came up to the surface. 18:45- Began MBES survey. 04-Sep-13-04:00 Stopped MBES survey. 9/4 12:00 (UTC+9h) N, E 08:00-08:42 Recovered transponder B. 08:54-10:43 Recovered transponder A. SE-5 (fresh breeze) 10:52-11:28 Recovered transponder C. 3 (sea slight) 12:47-20:34 MBES survey. Transit to off Chichi jima island for rigging. 05-Sep-13 08:00-09:30 Rigging dredge equipments. 9/5 12:00 (UTC+9h) 18:00-18:20 Scientists meeting. 17:14- Began MBES survey N, E ESE-3 (gentle breeze) 2 (sea smooth) 06-Sep-13-01:00 Stopped MBES survey. 9/6 12:00 (UTC+9h) N, E 08:10-11:46 Dredge operation DR :04-16:37 Dredge operation DR102. East-1 (light air) 18:10-18:45 Scientists meeting. 1 (calm) 18:52- Began MBES survey.

7 Date Local Time Event Position/Weather/ Sea condition 07-Sep-13-01:32 Stopped MBES survey. 9/7 12:00 (UTC+9h) N, E 07:54-12:23 Dredge operation DR :32-17:17 Dredge operation DR104. ESE-3 (gentle breeze) 19:12- Began MBES survey. 2 (sea smooth) 08-Sep-13 01:08 Finished MBES survey. 9/8 12:00 (UTC+9h) 07:48-11:28 Dredge operation DR :16-16:49 Dredge operation DR :33-18:54 Eight-figure turn N, E cloudy SE-3 (gentle breeze) 2 (sea smooth) 09-Sep-13 07:57-12:37 Dredge operation DR107. 9/9 12:00 (UTC+9h) N, E Transit to OKINAWA. ENE-1 (light air) 1 (calm) 10-Sep-13 Transit to OKINAWA. 9/10 12:00 (UTC+9h) N, E West-2 (light breeze) 1 (calm) 11-Sep-13 Transit to OKINAWA. 9/11 12:00 (UTC+9h) N, E East-3 (gentle breeze) 2 (Sea smooth) 12-Sep-13 09:00 Arrived at NAHA-shinko port, OKINAWA 8/7 12:00 (UTC+9h) OKINAWA Fig.3 KR13-14 ship track.

8 2. Backgrounds and objectives Metamorphic rocks associated with serpentinites have been found in the Ohmachi Seamount as the only locality of the eclogite facies rocks in the world ocean bottoms. Sea-floor exposure of these rocks provides composition, structure, and dynamics along deep subduction interface, where material transport is channelized ( subduction channel ), with minimal later modification by mountain building processes. Previously collected metamorphic rocks (five samples in 2001 and one in 2004) are drifted pebbles on debris apron at the foot of serpentinite exposures (YK K#609 R2, R4, R5, & R6), a presumably float stone on the rock exposure (6K#609 R12), or a dredged stone (KT04-28 D6-1). Two submersible dives (6K#1064 and 6K#1239) tried to find the outcrop of metamorphic rocks, however, nothing but serpentinites were found. Therefore, the mode of occurrence of metamorphic rocks, e.g. precise distribution of the rock bodies and contact relationships with serpentinites, have been still left unknown. One of the main purpose of this cruise is addressed to find and observe metamorphic rocks on outcrop using the ROV KAIKO 7000II. The target locality is 6K#609 Loc.4, where the collected sample (R12) were potentially derived from the same outcrop. Side-scan sonar equipped on the KAIKO launcher is used to find rock exposures, each of whose location is precisely determined by LBL. Two dives are taken to find the target, observe field occurrences of metamorphic rocks, collect samples, and measure orientation of metamorphic foliation. Another purpose is to increase volume and variation of rock types of metamorphic rocks. The volume of the previously collected metamorphic rock samples are limited ( kg for each sample is available) and insufficient for crushing and powdering at detailed geochemical and geochronological examinations. In addition, these samples are classified to three petrographic types, all of which underwent severe retrograde modification of rock textures and mineral chemistry. Increasing variation of rock types, as well as obtaining ones preserving early textures and minerals are necessary for precise analysis of metamorphic conditions and histories. For these purposes, dredges are performed around localities of metamorphic rocks. 3. Operation and preliminary results 3.1 Side scan sonar imaging In the first dive of this cruise (7K#608), the KAIKO launcher collected side scan sonar (SSS) images covering the survey area (Fig. 2). The launcher was towed along downslope (line 1) and upslope (line 3) transects, as well as line 2 connecting both the routes, all at a speed of 0.3 knot. Although only uncorrected SSS raster images were available onboard, they well contrasted relatively gentle middle slope terraces, steep and rocky lower slopes, a gravelly debris apron, and a mud-filled flat basin floor. In addition to these general topography, many more delicate features such

9 as abreast gullies and channels, their side walls, and intervening ridges were imaged. We compared these features with MBES bathymetric maps and previous 6K dive results, and finally selected the tip of a ridge with a pronounced reflection as the most probable identification for 6K# Loc.4. We set this point as the target for exploration of the 7K#609 dive. Fig.4 Position of transponders and the trail of side-scan sonar imaging during 7K#608 dive.

10 3.2 Dive report (7K#609 and7k #610) The purpose of these dives was to revisit the outcrop where a high pressure metamorphic rock (R12) was previously collected by the dive 6K#609 of (YK01-04) and to collect large amount of metamorphic rocks there. Two KAIKO7000II (7K#609 and7k #610) dives were conducted at the same outcrop. The VCL (dive 7K#609) firstly visited a large serpentinite (antigorite schist) outcrop (X:-904, Y:916, depth: 3374m) imaged by SSS data. However, we found out that it was not the target. The target outcrop was found in ~80 m north (X:-823, Y:920, depth: 3349m) from the first outcrop. We found that the target position was very close to the location estimated from the previous SHINKAI6500 dive (6K#609). We put two markers on the outcrop for the dive 7K#610 of the next day. Marker 1 and marker 2 were put on near the bottom of the outcrop and the upper part of it on a schistose plane of the serpentinite, respectively. We collected several rocks just on up and right sides of R12 collection site. We also collected two floats on mud slope in few meter lower part of it. We collected total 11 samples in this dive. In the dive 7K#610, we tried to go down just on the same outcrop. However, the VCL arrival position was 30m southwest of it (X: -867, Y: 916, depth: 3354m). In this dive, we continued sampling near R12 collection site and ~2m upper part of the outcrop. We collected total 9 samples Fig.5 7K#609 dive track.

11 including one huge sample (R104: ~49 kg). We measured a foliation plane of this outcrop using the top clinometer. Fig.6 7K#610 dive track. 3.3 Dredge We performed seven dredges, whose locations are listed in Table X, and the apparatus is shown in Fig. X, DR101. The operation followed the procedure as below: (a) The main wire length is held for three minutes at the depth where the dredger lies ca. 50 m above the estimated depth of the landing point. (b) After the position of the transponder is stabilized, the main wire is paid out. The vessel begins towing the dredger at a speed of ~0.5 knots. (c) The wire tension decreases at the time when the dredger landed on bottom. More 30 m (except for DR102 with 100 m) wires are released and then held. (d) When the transponder arrives around the target point, the vessel decreases its speed and then keeps its position as it stopped. The cable begins to be winched up at a speed of 10 m/min. (e) When the wire tension gradually increases and reaches to the break value of fuse wire, the cable stops to be winched up and is paid out at a speed of 30 m/min. After the wire tension decreases, the cable is winched up at a speed of 10 m/min, If the wire tension increases again, the same procedure is followed two to three times. In the case high wire tension cannot be

12 released with the above mentioned procedure, the vessel is backed to the landing point of the dredger, winching up the cable. (f) After the tension meter suggested that the dredger has left the bottom, the main wire is winched up faster at 20 and then 30 m/min. Off-bottom of the dredger can also be confirmed when the total wire length (main plus lead wires) becomes evidently shorter than the sea-floor depth, At the first two dredges (DR101 and 102), the on-bottom target was set around a fault scarp on the mud basin floor, where a float stone of epidote amphibolite (6K#609R002) was collected, and the end point was set around the outcrop where the garnet-zoisite amphibolite (6K#609R012) was collected. In both operations, the dredger began to be towed along the planned lines, however, left the bottom halfway without any significant hit before it reached to the end points. The hauls consisted of semi-consolidated sediments as well as soft mud at DR101, and only of soft mud at DR102. The on-bottom points for subsequent DR were placed on the approximate edges of the steep debris apron much closer to the outcrop, reflecting the results of DR101 and 102. In these later operations, the tension meter indicated significant and repetitive hits (and locking in cases) as the transponder passed through the end point, suggesting that the dredger arrived at rock exposures. Serpentinites and subordinate amounts of amphibolites were collected by these dredges. Date Dredge On bottom Off bottom Tension max. (JST) number Lat. Lon. Depth Lat. Lon. Depth (kn) 2013/9/6 DR N E 3, N E 3, /9/6 DR N E 3, N E 3, /9/7 DR N E 3, N E 3, /9/7 DR N E 3, N E 3, /9/8 DR N E 3, N E 3, /9/8 DR N E 3, N E 2, /9/9 DR N E 3, N E 3, MBES During the intervals of dives and dredges at night, bathymetry around the Ohmachi Seamount were mapped by KAIREI SeaBeam. The blank areas which had not yet been mapped in the survey area were almost fully filled with the acquired depth data. Together with the previous data, bathymetric features on and around the seamount were imaged enough for topographic analyses and for designing future surveys.

13 4. Summary Results of this cruise is briefly summarized as: (1) KAIKO 7000II vehicle successfully revisited to the same outcrop as 6K#609 Loc. 4 (the locality of an amphibolitized eclogite collected in 2001), whose location was aimed greatly relying on the side-scan sonar images newly acquired by the KAIKO launcher with LBL ecolocation. Two markers were left on the outcrop for future exploration. (2) Detailed observation and sampling concluded that this outcrop probably consists wholly of serpentinite. Two float stones of amphibolite collected from the outcrop surface close to a ridge crest suggested that the amphibolite exposure lies a little more upslope, where our exploration did not reached. (3) Repetitive dredges around 6K#609 Loc. 4 collected 44 new amphibolite samples of varying lithotypes as well as numerous antigorite schists. The largest block weighted ~9 kg voluminous enough both for various kinds of laboratory analysis. Precise positioning of the transponder attached to the main wire greatly helps to infer distribution of amphibolite bodies by lithotypes. (4) Detailed bathymetric map without blanks was completed on and around the Ohmachi Seamount. 5. Acknowledgements The scientific team thanks captain and crew of the R/V KAIREI, the KAIKO operation team, JAMSTEC Navigation Group, and scientific supports by Nippon Marine Enterprise Ltd. and Marine Works Japan Ltd. This study is supported by JSPS KAKENHI Grant no Notice on using this cruise report This cruise report is a preliminary documentation as of the end of the cruise. It may not be corrected even if changes on content (i.e. taxonomic classifications) are found after publication. It may also be changed without notice. Data on the cruise report may be raw or not processed. Please ask the Chief Scientist for the latest information before using.