IODP Expedition 366
Mariana Convergent Margin and South Chamorro Seamount
Daily Science Report for 6 February 2017
Location: In transit to Hong Kong
Science Update: The science party met for an end of expedition scientific summary meeting. The ship’s average speed today was 8.3 kt, with 52 nmi remaining to Hong Kong. On 7 February, the pilot came aboard at 0700 h and the first line was ashore at 0812 h, officially ending Expedition 366.
Daily Science Report for 5 February 2017
Location: In transit to Hong Kong
Science Update: The science party is finalizing the synthesis of their results for the expedition summary, and they are preparing for the end of the expedition. The science party met to discuss postcruise research. The ship’s average speed today was 9.8 kt, with 251 nmi remaining to Hong Kong.
Daily Science Report for 4 February 2017
Location: In transit to Hong Kong
Science Update: The science party is continuing to synthesize their results for the expedition summary. The laboratory groups have been meeting to discuss postcruise research, and the science party met to discuss end of expedition activities and for a presentation on mud volcanoes and their role in subduction zone’s water budget. The ship’s average speed today was 11.4 kt, with 486 nmi remaining to Hong Kong.
Daily Science Report for 3 February 2017
Location: In transit to Hong Kong
Science Update: The science party is finalizing writing up the results of Site U1498 and synthesizing the results from the expedition as a whole. The laboratory groups have been meeting to discuss postcruise research, and the science party met to discuss the location for the second postcruise meeting. Preparations are being made to ship the third party scientific instruments, the frozen microbiological samples, and other samples back to the scientists’ home institutions. The ship’s average speed today was 10.9 kt, with 760 nmi remaining to Hong Kong.
Daily Science Report for 2 February 2017
Location: In transit to Hong Kong
Science Update: The science party is continuing to write up the results of Sites U1497 and U1498, and is synthesizing the results from the expedition as a whole. The ship’s average speed today was 9.7 kt, with 1017 nmi remaining to Hong Kong.
Daily Science Report for 1 February 2017
Location: In transit to Hong Kong
Science Update: The science party is writing up the results of Sites U1497 and U1498, and synthesizing the results from the expedition as a whole. The ship’s average speed today was 11 kt, with 1250 nmi remaining to Hong Kong.
Daily Science Report for 31 January 2017
Location: In transit to Hong Kong
Science Update: The science party met to discuss the initial findings from Site U1498 and the tasks for the last week of the expedition. The towed magnetometer was deployed to take a magnetic profile from east to west across the Mariana arc, the Mariana Trough, the West Mariana Ridge, and the Perece Vela Basin. The scheduled arrival at the Hong Kong pilot station is 0700 h on 7 February, and today the ship’s average speed was 12 kt, helped by a following wind.
Daily Science Report for 30 January 2017
Location:
Hole U1498B (16°27.3716′N, 147°10.1166′E, water depth 3285 mbsl; proposed Site MAF-10B)
In transit to Hong Kong
Science Update: Downhole logging with the triple combo tool string reached 229 mbsf, 31 m from the base of the hole. Magnetic susceptibility, natural gamma radiation, resistivity, and temperature data were recorded for one downward pass and two upward passes of the tool string. The logging data cover the transition from the sediments to the overlying serpentinite mudflows, and up to the base of the drill pipe that was set at 52 mbsf. The tools were rigged down by 0530 h, and the drill pipe was raised back to the ship by 1250 h. The rig was secured and the transit to Hong Kong began at 1530 h.
Daily Science Report for 29 January 2017
Location: Hole U1498B (16°27.3716′N, 147°10.1166′E, water depth 3285 mbsl; proposed Site MAF-10B)
Science Update: Cores U1498B-21R to 27R penetrated 74 m and recovered 19 m (26%). Cores 21R to 23R are serpentinite mud with rock clasts, predominantly serpentinized ultramafic rocks. Cores 24R to 27R are nannofossil-bearing ash, which provides material to date the onset of the serpentinite mudflows at this location. We stopped drilling when the hole reached 260 mbsf, and the last core of the expedition came on deck at 1730 h. Enough operational time remained for downhole logging. The drill pipe was raised up to 52 mbsf and by the end of the day the triple combo tool string, comprising magnetic susceptibility, natural gamma radiation, resistivity, and caliper tools, was being lowered down the drill pipe.
Daily Science Report for 28 January 2017
Location: Hole U1498B (16°27.3716′N, 147°10.1166′E, water depth 3285 mbsl; proposed Site MAF-10B)
Science Update: Cores U1498B-15R to 20R penetrated 54 m to 186 mbsf and recovered 21 m (38%). These cores are serpentinite mud with ultramafic clasts, some as large as boulder size. The serpentinite muds are very firm but not lithified, and they are blue-grey with paler greenish thin bands of curved and randomly-oriented serpentinite. The ultramafic clasts are nearly all mildly to highly serpentinized harzburgites and dunites, and multiple generations of serpentinite viens can be observed in some of them.
Daily Science Report for 27 January 2017
Location: Hole U1498B (16°27.3716′N, 147°10.1166′E, water depth 3285 mbsl; proposed Site MAF-10B)
Science Update: Cores U1498B-9R to 14R penetrated 59 m and recovered 28 m (48%). These cores are serpentinite mud with ultramafic clasts, ranging up to boulder size. The serpentinite mud at these depths is becoming firm enough to be recovered by rotary core barrel (RCB) drilling.
Daily Science Report for 26 January 2017
Location: Hole U1498B (16°27.3716′N, 147°10.1166′E, water depth 3285 mbsl; proposed Site MAF-10B)
Science Update: The seafloor at the location of Hole U1498B was tagged with the drill pipe, and the tag was observed with the subsea camera to confirm the water depth and observe seafloor conditions on the lower slope of Celestial Seamount. Cores U1498B-1R to 8R penetrated 93 m and recovered 20 m of core (21%). These cores comprised mostly serpentinized ultramafic rocks, with a lesser amount of serpentinized mud. The RCB coring system preferentially recovers hard rocks in this environment.
Daily Science Report for 25 January 2017
Location: Hole U1498A (16°27.0898′N, 147°9.8502′E, water depth 3497 mbsl; proposed Site MAF-10B)
Science Update: Cores U1498A-9R to 19R penetrated 107 m and recovered 6.3 m of core (6%). These cores comprised nannofossil-bearing silt with volcanic ash, siltstones, and sandstones. Serpentinized ultramafic rock clasts were also found but they may have fallen from further up the hole. Following low recovery, we ended Hole U1498A at 182 mbsf and moved ~700 m upslope to the northeast, to a location where the serpentinite mud flows are thicker.
Daily Science Report for 24 January 2017
Location: Hole U1498A (16°27.0898′N, 147°9.8502′E, water depth 3497 mbsl; proposed Site MAF-10B)
Science Update: The drill string was lowered and tagged the seafloor at 3497 mbsl. At Site U1498 at the foot of the mud volcano, steep (~25%) slopes cause underestimated seafloor depths when calculated from PDR or the seismic seafloor reflection. Cores U1498A-1R to 8R penetrated 74.6 m and recovered 14.3 m of core (19%). Core 1R contained brown clayey silt with foraminifera; Cores 2R and 3R contained rock pieces up to 15 cm long including serpentinized ultramafic rocks, polymict breccia, and metabasite; and Cores 4R and 5R contained subhorizontally layered clast-poor serpentinite mud with sand. Below 45.4 mbsf, Cores U1498A-6R to 8R were almost empty and were drilled fast, indicating that we had penetrated softer material.
Daily Science Report for 23 January 2017
Location:
Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2019 mbsl; proposed Site MAF-9B)
In transit
Hole U1498A (16°27.09′N, 147°9.85′E [preliminary], water depth 3497 mbsl; proposed Site MAF-10B)
Science Update: Hole U1497D was reentered at 0325 h. The drill pipe was held at 24 mbsf, in the middle of the top joint of screened casing, and the water-sampling temperature-pressure tool (WSTP) was deployed to sample borehole fluids and take temperature measurements. In this hole, the water sample was mostly drilling fluid (seawater). The drill pipe was lowered further to check the location of the cement plug, now that it had time to harden. The top of cement was tagged at 103 mbsf, about 4 m above the base of the casing, thus the cement plug is well positioned to stop the formation entering into the casing. The ROV landing platform was deployed by freefall, landing on the reentry cone. On our previous visit to Site U1497 the beacon failed to release, so this time we fished it manually using a grappling hook that had been attached to the subsea camera frame for this purpose. This concluded operations at Site U1497. The drill pipe was raised to 1966 mbsl and the ship transited 6 nmi in dynamic positioning (DP) mode to Site U1498 (proposed Site MAF-10B) in 9 h, arriving at 2300 h. Site U1498 had been moved SW (downslope) from the prospectus location by ~1300 m to a location at the toe of the slope where the serpentinite mud flows are thinner and where we can reach the underlying pelagic sediments more easily in the remaining time. The science party met to discuss the initial findings from Site U1497.
Daily Science Report for 22 January 2017
Location:
Hole U1496C (18°6.6068′N, 147°6.1001′E, water depth 1244 mbsl; proposed Site MAF-11A)
In transit
Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2019 mbsl; proposed Site MAF-9B)
Science Update: The drill pipe was lowered down Hole U1496C and found fill at 99 mbsf, ~7 m above the base of casing, a depth similar to where it was when the casing was installed on 12 January. We sampled the material inside the casing with Cores U1496C-12G and 13G, which recovered 7.7 m serpentinite mud with lithic clasts from this previously cored depth interval. Five barrels of 14 ppg cement was pumped with the aim of sealing the base of casing. The drill pipe was raised above the seafloor and flushed, and then raised back to the ship, concluding operations at Site U1496. The 95 nmi transit to Hole U1497D took 9 h, arriving at 2045 h. The rig crew assembled the rotary core barrel (RCB) bottom-hole assembly and started to lower the drill pipe to the seafloor. The science party met for a presentation on seafloor ROV surveys of the Mariana region.
Daily Science Report for 21 January 2017
Location:
Hole U1492D (15°42.5694′N, 147°10.5991′E, water depth 3666 mbsl; proposed Site MAF-15A)
In transit
Hole U1496C (18°6.6068′N, 147°6.1001′E, water depth 1244 mbsl; proposed Site MAF-11A)
Science Update: We arrived at Hole U1496C at 1525 h after the 144 nmi, 13.4 h transit from Hole U1492D. The drill pipe was lowered to the seafloor and reentered Hole U1496C without difficulty, despite having to pass through the 32 inch diameter central aperture in the ROV landing platform. The drill pipe was lowered to 42 mbsf, within the upper joint of screened casing, where the water-sampling temperature-pressure tool (WSTP) was deployed to sample borehole fluids and temperature measurements. Initial geochemical measurements of the ~1 L WSTP fluid sample indicate that it was mostly formation water, mixed with some drilling water (seawater). The bottom-hole assembly included a 9.825 inch polycrystalline diamond compact (PDC) bit because it was narrow enough to fit inside the casing.
Daily Science Report for 20 January 2017
Location: Hole U1492D (15°42.5694′N, 147°10.5991′E, water depth 3666 mbsl; proposed Site MAF-15A)
Science Update: Hole U1492D was reentered at 0740 h with the purpose of hammering out the bridge plug which was blocking the casing. The bridge plug was tagged at 40 mbsf, and it was hammered using a custom-built tool over a period of 3 h before it moved downhole. The pipe was lowered and we relocated the bridge plug at 211 mbsf, just below the base of casing, thus the casing is now unblocked and ready for future deployment of a borehole monitoring observatory. The ROV landing platform was deployed by freefall, landing very close to being centered in the reentry cone. The base of casing was cemented with five barrels of 14 ppg cement; cementing is now the expedition’s preferred method of sealing the base of casing because of the risk that the mechanical bridge plugs set prematurely. By the end of the day the rig crew were raising the drill pipe to the ship. The science party met for a presentation on modeling of mud volcano build-up and heat flow, constrained by formation temperature measurements in the Mariana forearc.
Daily Science Report for 19 January 2017
Location:
Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2020 mbsl; proposed Site MAF-9B)
In transit
Hole U1492D (15°42.5694′N, 147°10.5991′E, water depth 3666 mbsl; proposed Site MAF-15A)
Science Update: The drill pipe reentered Hole U1497D and was lowered down to 105 mbsf, where five barrels of 14 ppg cement was pumped down to seal the bottom of the casing at that depth. The drill pipe was raised above the seafloor and the drill pipe was flushed to remove any residual cement. The bit was at the rig floor at 1540 h and the ship prepared for transit. The positioning beacon would not release from the seafloor, but we plan to return to Hole U1497D to check the location of the cement plug later in the expedition and we will try again to release the beacon. The 50 nmi transit to Hole U1492D (Blue Moon Seamount) took 5 h. The bridge plug hammer was prepared with the aim of unblocking the casing at Hole U1492D. The science party met for a presentation on fluids from clay dehydration and other sources in subduction zones.
Daily Science Report for 18 January 2017
Location: Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2020 mbsl; proposed Site MAF-9B)
Science Update: The casing was successfully installed to 107 mbsf in Hole U1497D by 1230 h. During the installation, it took ~5 h to pass below a difficult zone at ~40 m. Then at ~70 mbsf, the casing prereleased from the running tool, falling ~15 m further down the hole (a similar prerelease happened at Hole U1492D, earlier in the expedition), but we were able to continue washing and reaming down to the target depth. The hole was swept with high viscosity mud and the drill pipe and underreamer assembly was raised back up to the ship. In the evening, the rig crew assembled the bridge plug hammer parts, which will be required to unblock the casing at Hole U1492D, and assembled the cementing bottom-hole assembly for Hole U1497D. The science party met to present and discuss the initial science results from Site U1496.
Daily Science Report for 17 January 2017
Location: Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2020 mbsl; proposed Site MAF-9B)
Science Update: Having drilled out Hole U1497D to 120 m the previous day, the reentry cone was deployed by free-fall, then the drill pipe was raised back up to the ship. The casing was assembled and hung in the moonpool. The casing string is 106 m long and consists of three joints of 10.75 inch casing, three joints of screened casing, and three further joints of 10.75 inch casing. The regular casing joints underneath the screened section provide space for cement to seal the bottom of the casing to prevent the formation from entering. The mud motor and underreamer assembly was assembled, lowered through the casing string, and the running tool on the drill pipe was attached to the hanger at the top of the casing. The bit and underreamer extends ~4 m below the base of the casing. The whole assembly was lowered to the seafloor and Hole U1497D was reentered at 2310 h. By midnight, the bit had reached 25 mbsf.
Daily Science Report for 16 January 2017
Location: Hole U1497D (16°32.2548′N, 147°13.2621′E, water depth 2019 mbsl; proposed Site MAF-9B)
Science Update: Today Hole U1497D was deepened from 35 to 120 mbsf with the 14.75 inch bit at a slow but steady average rate of 7 m/h. The formation was firm and the hole appeared to be in good condition, apart from a difficult zone in the upper part of the hole, perhaps related to loose sand and gravel observed in Hole U1497A between 23–26 mbsf. The hole was swept with 50 barrels of high viscosity mud to prepare for installing the screened casing.
Daily Science Report for 15 January 2017
Location:
Hole U1497C (16°32.2504′N, 147°13.2500′E, water depth 2019 mbsl; proposed Site MAF-9B)
Hole U1497D (16°32.25′N, 147°13.26′E, water depth 2020 mbsl; proposed Site MAF-9B)
Science Update: Hole U1497C was started at 1145 h with a 14.75 inch bit; the aim was to drill down to about 100 mbsf and then deploy screened casing for future borehole monitoring at this site. We stopped this hole at ~11 mbsf because of high torque and slow penetration. For a second attempt at 100 m, we started Hole U1497D at a location closer to where Holes U1497A and U1497B had achieved reasonable penetration depths. By the end of the day Hole U1497D reached 35 mbsf.
Daily Science Report for 14 January 2017
Location:
Hole U1497A (16°32.2538′N, 147°13.2641′E, water depth 2020 mbsl; proposed Site MAF-9B)
Hole U1497B (16°32.2528′N, 147°13.2606′E, water depth 2019 mbsl; proposed Site MAF-9B)
Science Update: Cores U1497A-6F to 13G reached 37.9 mbsf, penetrated 17.5 m, and recovered 12.8 m of core (73%). These cores contained a diverse range of material, including dusky red polymict breccia with both serpentinite and carbonate components, fairly well-sorted clast-supported polymict ranging in grain size from fine sand to gravel to pebble, and bluish serpentinite mud with serpentinized rock clasts. Cores U1497B-1F and 7F penetrated 23.8 m and recovered 20.2 m of core (73%), and contained a similar sequence of materials to Hole U1497A. At the end of the day Hole U1497B was terminated and the drill pipe was being raised back to the ship.
Daily Science Report for 13 January 2017
Location: Hole U1497A (16°32.2538′N, 147°13.2641′E, water depth 2020 mbsl; proposed Site MAF-9B)
Science Update: The 94 nmi transit to Site U1497 took 9 h. Site U1497 is located near the summit of Celestial (Fantangisña) Seamount, and is known from previous ROV dives to have more surface boulders and cobbles than the other two seamounts drilled on this expedition. Prior to starting the hole, we surveyed the seafloor with the subsea camera to find preferred coring locations with fewer surface rocks. Cores U1497-1F to 5F penetrated 16.7 m and recovered 11.0 m of core (67%). Cores U1497-1F to 5F contained a 45 cm layer of pelagic muddy sand overlying matrix-supported serpentinite breccia.
Daily Science Report for 12 January 2017
Location: Hole U1496C (18°6.6074′N, 147°6.1000′E, water depth 1244 mbsl; proposed Site MAF-11A)
Science Update: The casing and bit/underreamer assembly reentered Hole U1496C at 0130 h, and reached the target depth of 109 mbsf at 1100 h. Downward progress was fairly rapid, apart from taking a few hours to pass through a hard zone at ~40 mbsf. The casing was latched to the reentry cone and the bit/underreamer assembly was pulled inside the casing. The ~4 m diameter circular ROV platform was deployed and landed slightly off-center but still functional. Hard fill was found in the casing at a depth of 99 mbsf, indicating that formation material had come up 6 m inside the casing. The drill pipe was raised up to the ship and the rigfloor was secured for transit to Site U1497 (proposed Site MAF-9B) on Celestial Seamount.
Daily Science Report for 11 January 2017
Location: Hole U1496C (18°6.6074′N, 147°6.1000′E, water depth 1244 mbsl; proposed Site MAF-11A)
Science Update: Hole U1496C was widened by drilling and reaming to 120 mbsf with a 14.75 inch bit, to prepare the hole for casing. The drill pipe was raised up to the drill floor and the 105 m long casing was assembled. It consists of two regular 10.75 inch casing joints, three screened casing joints, and three further regular casing joints, connecting to a 16 inch casing hanger at the top. The underreamer and mud motor bottom-hole assembly (BHA) was assembled and lowered through the casing, and the running tool on the BHA was attached to the casing hanger on the casing. By the end of the day the whole assembly was being lowered to the seafloor. The science party met to discuss the science results from the flank of Big Blue Seamount, Sites U1493, U1494, and U1495.
Daily Science Report for 10 January 2017
Location: Hole U1496C (18°6.6074′N, 147°6.1000′E, water depth 1244 mbsl; proposed Site MAF-11A)
Science Update: Cores U1496C-1R to 11R penetrated 105 m and recovered 8.52 m (8%). Cores U1496C-1R and 11R contained serpentinite mud with rock clasts, and Cores U1496C-5R and 7R contained ultramafic rock clasts with serpentinite veins; the other cores were empty. The low levels of core recovery were anticipated for rotary coring in this material, but the coring did its intended job of reaching 105 mbsf, the depth to which casing will be emplaced in Hole U1496C. The hole was swept and reamed, the reentry cone was deployed, and the drill pipe was raised back to the ship. At the end of the day, the hole was reentered with a 14.75 inch bit to widen the hole for drill-in casing.
Daily Science Report for 9 January 2017
Location:
Hole U1496B (18°6.6210′N, 147°6.1000′E, water depth 1240 mbsl; proposed Site MAF-11A)
Hole U1496C (18°6.6074′N, 147°6.1000′E, water depth 1244 mbsl; proposed Site MAF-11A)
Science Update: Cores U1496B-7F to 10F penetrated 10.6 m and recovered 3.8 m of core (36%), comprising light greenish grey serpentinite mud with rock clasts. The recovered clasts reach as large as cobble size, and a clast-rich zone starting at about 28 mbsf slowed coring. To try to pass through the zone we took XCB Core U1496B-8X, then drilled ahead to 34.3 mbsf, and took HLAPC Core U1496B-10F which contained only rock clasts. To reach the target depth of about 110 mbsf for the emplacement of screened casing at this site, we pulled the drill pipe back up to the ship to switch to RCB rotary coring. By the end of the day, the first core from Hole U1496C had been taken.
Daily Science Report for 8 January 2017
Location:
Hole U1496A (18°6.5936′N, 147°6.0999′E, water depth 1244 mbsl; proposed Site MAF-11A)
Hole U1496B (18°6.6210′N, 147°6.1000′E, water depth 1240 mbsl; proposed Site MAF-11A)
Science Update: Hole U1496A (MAF-11A) was started at 0045 h after the 1 nmi transit from Site U1495. Cores U1496A-1F to 11X penetrated 42.8 m and recovered 38.7 m (90%). Cores U1496B-1F to 6F penetrated 25.4 m and recovered 19.1 m (75%). These cores are pale greenish-grey serpentinite mud with partly serpentinized ultramafic rock clasts. The rock clasts become more abundant in the lower part of these holes, causing penetration rate to slow. At Hole U1496A, we first switched from half-length APC to XCB coring with Core U1495A-11X, but when penetration rate became very slow we decided to move 50 m to the north to start Hole U1496B. The cores contain gas, apparent as voids which open up in the core on the catwalk, and include hydrogen. The pH of interstitial waters reaches a plateau of about 12.4 at shallow depth, indicating active fluid flow from depth at this location.
Daily Science Report for 7 January 2017
Location:
Hole U1495A (18°5.6693′N, 147°6.0004′E, water depth 1405 mbsl; proposed Site MAF-12B)
Hole U1495B (18°5.6788′N, 147°5.9901′E, water depth 1402 mbsl; proposed Site MAF-12B)
Science Update: The ship arrived on location at Site U1495 at 0115 h. Cores U1495A-1F to 5G penetrated 10.7 m and recovered 5.28 m of core (49%). Cores U1495B-1F to 6F penetrated 10.8 m and recovered 10.8 m of core (100%). These cores are serpentinite mud with serpentinized ultramafic rock clasts, overlain by a thin (<40 cm) layer of sandy silt. The serpentinite muds were very firm, and the holes were unstable for drilling. After each half-length APC (HLAPC) core an XCB barrel was run while drilling down to the depth of the previous HLAPC core, resulting in four “ghost cores” from this site containing mostly rock clasts. Elevated levels of hydrogen were found Core U1495A-2F, so we decided to drill Hole U1495B to increase the number of microbiological and interstitial water samples from this site.
Daily Science Report for 6 January 2017
Location: Hole U1494A (18°3.0900′N, 147°6.0000′E, water depth 2200 mbsl; proposed Site MAF-13A)
Science Update: Cores U1494A-1F to 11X penetrated 39.0 m and recovered 29.6 m of core (76%). These cores are mostly bluish-grey to pale greenish serpentinite pebbly mud. In Core U1494A-2F there is a 2 m layer of sandy silt with foraminifera, which likely marks a boundary between serpentinite mud flows. The serpentinite mud at Site U1494 was very firm and had relatively low water content compared to muds at equivalent depths at the other Expedition 366 sites. There was pervasive deformation of Cores 6F to 10F, with mud and rock clasts sucked-in and sheared along the length of core sections. Coring by half length APC and by XCB became progressively more difficult with depth, and after Core U1494-11X took 2 h to drill, we decided to move on to Site U1495, proposed Site MAF-12B. At the end of the day we were underway in dynamic positioning (DP) mode to Site U1495, located 5 km north at the edge of the summit area of Big Blue Seamount.
Daily Science Report for 5 January 2017
Location:
Hole U1493B (17°59.1665′N, 147°6.0060′E, water depth 3359 mbsl; proposed Site MAF-14A)
Hole U1494A (18°3.0900′N, 147°6.0000′E, water depth 2200 mbsl; proposed Site MAF-13A)
Science Update: Cores U1493B-4F to 9X penetrated 17.5 m (15.1 to 32.6 mbsf) and recovered 12.9 m of core (74%). These cores are bluish serpentinite mud with serpentinized ultramafic clasts. An APCT measurement was made on Core U1493B-5F. Because of difficult APC/XCB drilling conditions and because we had sufficient samples for lithological, geochemical, and microbiological assessment of the site, we decided to move 4 nmi upslope to Site U1494. The transit was made in dynamic positioning (DP) mode at a speed of about 1 kt, and the first core at Hole U1494A was taken at 2325 h.
Daily Science Report for 4 January 2017
Location:
In transit to Site U1493 (proposed Site MAF-14A)
Hole U1493A (17°59.1668′N, 147°6.0057′E, water depth 3359 mbsl; proposed Site MAF-14A)
Hole U1493B (17°59.1665′N, 147°6.0060′E, water depth 3359 mbsl; proposed Site MAF-14A)
Science Update: We arrived at Site U1493 at 0400 h following a 13 h transit. A reentry cone was set up in the moonpool, and the drill pipe was lowered through it. The reentry cone will be used at proposed Site MAF-11A at the summit of Big Blue Seamount, but we needed to set up the cone around the drill pipe now because the same drill string will be used, without being raised back up to the ship, at Site U1493 and proposed Sites MAF-13A, 12B, and 11A. These sites form a ~14 km south to north transect, and are close enough for transit between them in dynamic positioning (DP) mode. Core U1493A-1H recovered 10 cm of mud with microfossils. On this core, the APC core barrel bent in two places, so we offset 10 m to the east to start Hole U1493B. Cores U1493B-1H, 2X, and 3F reached 15.1 mbsf and grade downwards from yellow-brown mud with microfossils to pale greenish serpentinite mud to bluish serpentinite mud, with rock clasts in the serpentinite muds.
Daily Science Report for 3 January 2017
Location:
Hole U1492D (15°42.57′N, 147°10.60′E, water depth 3666 mbsl; proposed Site MAF-15A)
In transit to Site U1493 (proposed Site MAF-14A)
Science Update: After an unsuccessful attempt to unseat the bridge plug, it remained stuck at 37 mbsf. The drill pipe was detached from the bridge plug and the drill pipe was raised back to the ship, where the bridge plug release tool was inspected. Our options for preparing for future borehole monitoring system at Site U1492 are to mill out the bridge plug, or to drill in a second (shorter) casing sting in a new hole. Since either option requires some preparation time, we decided to transit 136 nmi north to Site U1493 (proposed Site MAF-14A) at the foot of Big Blue Seamount, and return to Site U1492 later in the expedition. The thrusters were raised and the transit began at 1430 h. The science party met for two presentations, one on the IODP drillship Chikyu, and one on microbial life associated with a terrestrial active serpentinization site.
Daily Science Report for 2 January 2017
Location: Hole U1492D (15°42.57′N, 147°10.60′E, water depth 3666 mbsl; proposed Site MAF-15A)
Science Update: We were able to wash the drill bit from the seafloor down to the base of the casing at 211 mbsf. No obstructions were found and a high viscosity mud sweep made sure the hole was clear. The drill string was raised back to the ship, the bottom part was exchanged to include the bridge plug deployment apparatus, and it was lowered back down into the hole. The bridge plug was to be set near the base of the casing to prevent formation muds from coming up into the casing. However, at 2300 h, the bridge plug set prematurely at 37 mbsf while adding a pipe joint, apparently due to high ship heave. We are recovering the drill string and discussing our options. The science party met for a presentation on the setting and aims of the upcoming four sites at Big Blue Seamount (from the foot of the slope to the summit, these sites are MAF-14A, 13A, 12B, and 11A).
Daily Science Report for 1 January 2017
Location: Hole U1492D (15°42.57′N, 147°10.60′E, water depth 3666 mbsl; proposed Site MAF-15A)
Science Update: In the morning, the rig floor crew pulled the drill string back up to the ship and laid out the casing running tool, mud motor, underreamer, and bit. The underreamer was serviced and cleaned of rocks and mud. As part of regular maintenance, 115 ft of drilling line was slipped and cut. In the evening, the drilling bottom-hole assembly was lowered to the seafloor in preparation for cleaning out any material that may be inside the casing. The science party attended a presentation about olivine crystal fabrics in peridotite, with examples from the northern Mariana Trench and worldwide.