IODP Expedition 360
SW Indian Ridge Lower Crust and Moho
Daily Science Report for 31 December 2015
Location: Underway from Site U1473 towards Mauritius for a medical evacuation.
Science Update: While underway towards Mauritius for a medical evacuation, all laboratory teams continue to generate data from discrete samples, make final edits to Methods and Site 179-1105 report sections, and plan Site U1473 reports.
In selected thin sections from Cores U1473A-26R to 29R that show moderate to substantial alteration intensity, olivine shows more intense alteration than pyroxene and plagioclase, usually developing typical mesh texture. Clinopyroxene is altered into amphibole. Plagioclase is mostly replaced by secondary plagioclase with some chlorite occurring in the cleavages and along the boundary. Clay minerals occur more or less in all the primary minerals. In thin sections from Cores 2R–32R selected to study crosscutting relationships, thin shear bands crosscut an earlier crystal plastic fabric in several samples. For example, in Section 20R-1 a subvertical shear band is cut by a subhorizontal mylonite. In other examples, subhorizontal crystal plastic fabrics are cut by thinner subvertical shear bands. These relationships suggest multiple episodes of deformation.
The Physical Properties team continued their measurements on the remaining discrete samples, with the following results: compressional velocity, Vp, for 66 samples ranges from 5936 to 7138 m/s and averages 6735 m/s; Vp anisotropy for the same 66 samples ranges from 0.4% to 10.9% and averages 2.7%; grain density for 60 samples ranges from 2.88 to 3.13 kg/m3 and averages 2.97 kg/m3; porosity for the same 60 samples ranges from 0.1% to 2.9% and averages 0.8%.
Daily Science Report for 30 December 2015
Location:
Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Underway towards Mauritius for a medical evacuation
Science Update: The stuck pipe was freed at 0100 h, after working it for a total of 3 h with excessive torque and pull, and we retrieved Core U1473A-44R (400.5–410.2 mbsf) with a recovery of 5.4 m (56%). An attempt to clean the hole back to the bottom, including a 45 barrel mud sweep, experienced difficulties and we decided to retrieve the drill string and inspect the bit. The bit cleared the seafloor at 0740 h and was missing three of its four cones. A new bottom-hole assembly (BHA) was made up with a 9 inch Bowen fishing magnet and deployed to the seafloor in an attempt to recover the cones and allow further coring in Hole U1473A. The hole was reentered at 1244 h and the fishing tool was lowered and washed to the bottom of the hole by 1700 h. After executing the Bowen procedure for recovering metal parts in the hole, the drill string and fishing tool were retrieved, clearing the rig floor at 2020 h. No bit cones were recovered. By this time a medical evacuation had been initiated. The BHA was laid out to the drill collar racks and the thrusters were raised in preparation for the transit, and the ship departed towards Mauritius at 2330 h.
All remaining core descriptions were completed for the interval cored so far (Cores U1473A-2R through 44R). Cores 43R to 44R consist mostly of coarse-grained subophitic olivine gabbro with rare horizons enriched in oxide and display a granular texture. Several felsic veins were also observed. Cores 40R to 44R have background alteration intensities that vary randomly, often related to veins. Most metamorphic veins are filled with carbonate. Amphibole veins, which were very commonly observed in the upper section of Hole U1473A, are very rare in these cores. Felsic veins are mostly leucodiorites, which are in general more intensely altered than the hosting gabbro. Core 44R has irregularly developed grain size layering. The magmatic fabrics are weakly developed and inclined. Crystal plastic fabrics are locally developed, incipient, and have a shallow dip. A felsic vein in Section 44R-1 is offset by ~3 mm with a reverse sense of shear. Carbonate veins are inclined or subhorizontal.
The petrophysics team continued their measurements on whole-round sections, section halves, and discrete samples. Compressional seismic velocities (Vp) measured in 52 gabbroic samples at room pressure and temperature along three perpendicular directions, range from 5930 to 7110 m/s (average 6730 m/s; average standard deviation 25 m/s). The apparent anisotropy of Vp is 2% on average. Density and porosity were measured on 45 samples. Grain density ranges from 2.88 to 3.13 g/cm3 (2.96 g/cm3 average). Porosity ranges from 0.10% to 2.90% (0.84% average). Thermal conductivity was measured on pieces from archive section halves. It is 2.18 W/(m·K) on average with a standard deviation of <2% (0.6% on average).
Daily Science Report for 29 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: Today we recovered Cores U1473A-40R through 43R (361.7–400.5 mbsf) with a total recovery of 22.6 m (58%). At 2200–2400 h, while cutting Core 44R, high torque and pull was encountered and attempts were made to free the pipe, which included a 30 barrel mud sweep at 408 mbsf.
Cores 38R to 42R (342.3–390.8 mbsf) consist mostly of coarse-grained subophitic to granular olivine gabbro. Very rare deformed horizons contain oxides. A diabase interval ~2 m thick occurs in Sections 42R-1 and 2 (381 mbsf). One piece of this diabase has felsic material at its contact with the host gabbro, and the felsic material locally intrudes the diabase; no chilled margin was observed. Several felsic veins and patches occur.
In Cores 35R to 40R (313.2–371.4 mbsf), the background static alteration varies randomly and increases with increasing veining intensity. The thin section observations enabled us to depict a crystal-plastic evolution under granulite to amphibolite facies metamorphic conditions. We also recognized that: (i) the earliest amphibole veining event occurred in the amphibolite facies and generated a cm scale halo in the host gabbros; and (ii) the injection of the felsic veins most likely occurred during the cooling of the host gabbro from granulite to amphibolite facies conditions.
Cores 40R through 43R (361.7–400.5 mbsf) have weaker crystal-plastic fabrics than the cores above this interval, but locally contain decimeter to meter scale zones of well-developed protomylonitic and mylonitic foliation. Discrete cm wide shear bands crosscut the distributed crystal plastic fabric at high angles. In one example from Section 40R-1, a moderately dipping weak crystal plastic fabric is crosscut by a subvertical shear band. On one side of the shear band the original crystal plastic fabric is bent into the shear zone, whereas the other contact is sharp. At least two generations of leucocratic veins occur. The first, higher temperature generation has diffuse and complicated margins with the gabbro and is intimately associated with the shear zone deformation. A second lower temperature generation crosscuts the gabbro with sharp boundaries. Alteration veins are characterized by open fractures partially to completely filled with carbonate.
The paleomagnetic team completed thermal demagnetization of the first set of discrete samples from Hole U1473A. The majority of samples are characterized by a high stability remanence that unblocks between 500°–580°C, indicating magnetization carried by magnetite. Other samples have more distributed unblocking, suggesting presence of a wider range of magnetic grain sizes or remanence components carried by titanomagnetite in oxide-rich rocks.
The petrophysics team continued their measurements on whole-round sections, section halves, and discrete samples. High magnetic susceptibilities measured on whole-round sections and section halves are related to high Fe-Ti oxide contents in the rocks. Natural gamma radiation (NGR) is in general very low (<1 count/s on average), as classically observed in oceanic gabbros; a few peaks in the NGR logs (up to ~10 counts/s) correspond to felsic intervals in the core.
The microbiology team processed three more samples and ran another contamination test of core samples with drilling tracer.
Daily Science Report for 28 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: We reentered Hole U1473A with the third RCB bit at 0015 h, washed out 1.5 m of fill in the bottom of the hole, and continued RCB coring at 0315 h. We recovered Cores U1473A-35R through 39R (313.2–361.7 mbsf) with a total recovery of 21.4 m (44%).
Cores 33R to 37R show either primary magmatic textures or granular texture when deformed. Grain size varies from medium- to coarse-grained. The dominant lithology is olivine gabbro with some rare intervals containing small amounts of oxide or lower amounts of olivine. Felsic veins and patches were also observed. The background static alteration intensity in Cores 30R to 34R is generally slight, and extensive in intervals with vein networks. High-temperature recrystallization associated with plastic deformation and amphibole veins is less abundant, whereas low-temperature clay and carbonate veins with clay-rich halos are more dominant, compared with shallower cores. The olivine gabbro in Cores 35R to 39R is variably deformed. In Core 35R, grain size changes define shallow to moderately dipping mylonites with crosscutting intrusions. In Core 36R, the crystal plastic fabric is weaker and steeper. Micrograbbro crosscuts the earlier crystal plastic foliation. Core 37R has a weaker crystal plastic fabric and several felsic network veins. Section 39R-4 has an ultramylonite in contact with a brecciated leucocratic zone. Two fault breccias were identified in Sections 35R-2 and 37R-3. The microbiology team detected ATP in several samples, primarily those taken from veins; the origin of the ATP will have to be determined on shore.
Daily Science Report for 27 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: Today we recovered Cores U1473A-30R through 34R (264.7–313.2 mbsf) with a total recovery of 29.0 m (60%). Three high viscosity mud sweeps were pumped during coring in this interval. At 1630 h, after retrieving Core 34R, the drill pipe was pulled for a bit change, clearing the rig floor at 2055 h. By midnight the fourth RCB bit was back near the seafloor and ready for reentry into Hole U1473A.
Cores 28R to 32R mostly have primary magmatic textures and are coarse-grained. The dominant lithology is olivine gabbro with subordinate disseminated-oxide and oxide-bearing olivine gabbro. Numerous felsic veins or patches are observed. One intrusion of granoblastic microgabbro may represent part of a dike close to its root zone. Enclaves of similar material are observed in association with felsic veins and are also included within subophitic olivine gabbro. In Cores 25R to 29R, background static alteration is variable, ranging from slight to extensive. Intense alteration occurs in intervals with heavy veining. Brownish red clays after olivine are conspicuous. Preliminary results from XRD analysis show the occurrence of different clay minerals as secondary products in some veins and primary minerals. The deformation intensity is much lower in Cores 28R–34R than in previous cores. In some zones grain size varies in irregular patches; in other local zones grain size variations are overprinted by a crystal plastic fabric. The fabrics have a consistently moderate to shallow dip. Shear bands 1–2 mm thick locally crosscut deformed and undeformed gabbro. Felsic vein networks locally form magmatic breccias. A fault breccia with a very fine grained clay matrix occurs in Section 31R-1. The majority of alteration veins are filled with carbonate, form parallel sets, and are inclined.
The petrophysics and paleomagnetics teams continued their measurements on whole-round sections and section halves, and all laboratory teams kept sampling the cores for shipboard preparation and analysis of discrete samples.
Daily Science Report for 26 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: Today we recovered Cores U1473A-24R through 29R (206.5–264.7 mbsf) with a total recovery of 31.1 m (53%). A 30 barrel high viscosity mud sweep was pumped at 262 mbsf while cutting Core 29R.
Cores 23R through 27R are partially deformed, medium to coarse-grained olivine gabbro and subordinate disseminated-oxide gabbro with granular texture and some felsic patches and veins. Cores 21R through 24R have slight to extensive background alteration associated with veins. An extensive felsic vein network continued from Core 23R into 24R, disrupting the crystal plastic fabric and in some places forming a magmatic breccia. Mylonites are present throughout Cores 24R through 26R and enclose a small block of very coarse grained to pegmatitic olivine gabbro. The coarse grained gabbro exhibits semi-brittle deformation and is bound by a subvertical mylonite. Below the coarse grained interval, a 10 m thick zone of subhorizontal mylonites grades into medium to coarse grained weakly foliated gabbro in Core 27R. Alteration veins are commonly filled with carbonate and quartz, forming parallel sets. Amphibole veins are observed in mylonitic zones crosscutting the fabric at high angles. Brittle deformation is distributed over broad zones of minor fracturing in plagioclase and pyroxene.
Thin sections of the interval recovered to date show different alteration types of olivine. Most of the olivine is altered into brown clay under low temperature and some is altered into talc with minor green amphibole under relatively high temperature.
The petrophysics and paleomagnetics teams continued their measurements on whole-round sections and section halves, and all laboratory teams kept sampling the cores for shipboard preparation and analysis of discrete samples.
Daily Science Report for 25 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: We waited for the heave to subside until 1015 h, reentered Hole U1473A at 1122 h, and resumed coring at 1400 h. We subsequently recovered Cores U1473A-21R through 23R (180.1–206.5 mbsf) with a total recovery of 9.7 m (37%).
Cores 20R to 22R consist of deformed, coarse-grained olivine gabbro and disseminated-oxide gabbro with granular texture and a few felsic patches. Cores 19R to 20R show slight to substantial background alteration, often related to veins. In Cores 21R and 22R the crystal plastic fabric is weaker compared to cores described earlier. In Core 22R, a felsic vein network is associated with highly altered zones of albitized feldspar within the host rock, forming the locus of later low temperature alteration and brittle deformation. One felsic vein is offset by a reverse-sense brittle fault. Core 23R has a distinctive meter scale zone of mylonites cut by later discrete shear bands at a high angle. Displacement along the shear bands has led to the development of a pull-apart structure filled with felsic material. The alteration veins are mostly filled with carbonate and are inclined.
Continued observation of thin sections from Cores 2R to 14R revealed that some of the amphibole veins represent two evolutionary stages: the formation of nearly monomineralic veins of brown-green amphibole at high temperatures, and a second stage of greenshist mineral formation including zoisite, colorless amphibole, and chlorite.
The petrophysics and paleomagnetics teams continued their measurements on whole-round sections and section halves, and all laboratory teams kept sampling the cores for shipboard preparations and analysis of discrete samples.
Daily Science Report for 24 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: Today we recovered Cores U1473A-18R through 20R (158.0–180.1 mbsf) with a total recovery of 9.1 m (41%). After Core 18R was recovered, the pipe was tripped to the surface and redeployed with a new bit (0400–1415 h). At 1900 h, while we were drilling Core 20R, the heave compensator reached full stroke and the bit couldn’t be kept on the bottom of the hole. We therefore suspended drilling operations. The pipe was pulled clear of Hole U1473A at 2100 h and suspended from the rig floor with the bit at 635 mbrf. The ship was offset 30 m to the east of Hole U1473A while waiting for conditions to improve.
Cores U1473A-16R to 19R are granular and consist mostly of olivine gabbro with subordinate olivine oxide gabbro. The grain size is variable and layers of fine- to medium-grained gabbro alternate with coarser-grained gabbro. Most of the recovered rocks are strongly deformed and the original grain size and texture are probably erased. Some very rare felsic veins were observed. Preliminary studies of the first thin sections from Hole U1473A material indicate dynamic crystallization of brown and green amphibole and subsequent development of veins mostly consisting of green amphibole. These occurrences are presumably related to reactions of gabbroic rocks with H2O-rich agents under amphibolite facies metamorphic conditions. Primary igneous layering is observed in Cores 17R–19R and is overprinted by a moderately to shallowly dipping crystal plastic fabric. The grain size layering is subparallel to the shear bands. In Core 20R the crystal plastic fabric is defined by porphyroclastic shear zones, which have near-vertical dips. The vertical crystal plastic fabrics are crosscut and offset by more discrete mylonites that have a moderate dip. Core 19R has several inclined carbonate veins and 1–5 mm thick bands of cataclasite that overprint the crystal plastic fabrics.
The petrophysics and paleomagnetics teams continued their measurements on whole-round sections and section halves, and all laboratory teams kept sampling the cores for shipboard preparations and analysis of discrete samples.
Daily Science Report for 23 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: We recovered Cores U1473A-14R through 17R (119.2–158.0 mbsf) with a total recovery of 27.1 m (70%).
Cores U1473A-13R to 15R consist mostly of medium to coarse-grained subophitic olivine gabbro with subordinate coarse-grained subophitic disseminated-oxide olivine gabbro. Some rare coarse-grained subophitic oxide-bearing olivine gabbro, and medium-grained granular olivine-bearing gabbro are also observed. Medium-grained gabbro layers are locally embedded within coarser grained gabbro. Rare felsic veins are present. In Cores 11R to 14R, alteration minerals generally make up <30% of total rock volume. Locally, particularly in vein halos, they make up 50%–60%. Many amphibole and plagioclase veins have textures that indicate crystallization over igneous and metamorphic regimes. Variably developed primary igneous layers, defined by grain size variations from coarse to fine grained, are observed throughout the interval. The contact between grain size layers is often irregular and subparallel with the cross-cutting crystal plastic fabric. The crystal plastic fabric is moderately to shallowly dipping and occurs in decimeter intervals with a few high intensity intervals. The magmatic fabrics are weakly developed, defined by plagioclase and pyroxene, and inclined. The alteration veins are steeply dipping and filled with amphibole surrounded by halos. The amphibole veins sometimes form faults displacing the crystal plastic fabric.
In addition to the ongoing description of cores by the igneous petrology, metamorphic petrology, and structural geology teams, the petrophysics, paleomagnetics, geochemistry, and microbiology teams continued their sampling and measurement routines in Cores 11R though 17R.
Daily Science Report for 22 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: We recovered Cores U1473A-10R through 13R (80.4–119.2 mbsf) with a total recovery of 21.0 m (54%).
Cores U1473A-10R to 12R consist mostly of coarse-grained granular olivine gabbro (two-thirds of recovered rocks), with subordinate medium-grained granular disseminated-oxide olivine gabbro (23% of recovered rocks). Nearly all of the rocks suffered plastic deformation. Rare oxide gabbro is observed and displays a coarse-grained granular texture. One small intrusion of amphibole oxide gabbro (medium-grained, granular), and two veins of coarse-grained amphibole-rich diorite were observed. Static background alteration intensity in Cores 8R–10R is mostly slight, with intervals of moderate to substantial alteration associated with the occurrence of veins and lithological contacts. Olivine is generally the most heavily altered primary mineral and is conspicuously replaced by brownish red clay. The crystal plastic fabrics have changed dip between Cores 9R and 10R, with 9R and above being steeply dipping and 10R and below having moderate to shallow dips. The crystal plastic fabrics overprint alternating layers of fine to coarse grained gabbro, possibly original layering with a magmatic fabric. The crystal plastic fabric intensity ranges from gneissic to mylonite in discrete intervals. The alteration veins are filled with amphibole, form parallel sets, and crosscut the crystal plastic fabric. Brittle deformation often overprints the crystal plastic fabrics. Several fractures with moderately plunging slickenlines were also observed.
The petrophysics and paleomagnetics teams measured magnetic susceptibility, GRA density, and magnetic remanence of Cores 10R through 12R using core logging systems and thermal conductivity on core pieces. They also started measurements of density and magnetic remanence on discrete subsamples. The microbiologist processed samples from Cores 10R to 14R and conducted contamination tests on subsamples from the exterior and interior of a core subjected to a tracer during coring.
Daily Science Report for 21 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: We recovered Cores U1473A-7R through 9R (51.3–80.4 mbsf) with a total recovery of 12.8 m (44%). After Core 9R was recovered, the drill pipe was tripped to the surface for a bit change, arriving at the rig floor at 1940 h. The new bit was installed and lowered to the seafloor, the camera system was deployed, and Hole U1473A was reentered for the second time at 2325 h.
Cores 6R to 9R consist mostly of coarse-grained subophitic olivine gabbro with minor olivine gabbro containing <5% oxides. Two-thirds of olivine gabbro are coarse-grained and subophitic, while one-third is medium grained, granular, and strongly deformed. One magmatic contact was observed between an olivine gabbro and an olivine oxide norite. An altered diabase crosscuts the section. The alteration intensity in Cores 4R to 7R was slight to substantial, and the alteration minerals are amphibole, chlorite, and brownish clay. Several structural contacts between deformed and undeformed olivine gabbro were observed. These are usually moderately to steeply dipping porphyroclastic and mylonitic shear zones defined by layers of recrystallized plagioclase. In some cases both the shear zone and its adjacent damage zone are visible, providing a complete transect from undeformed gabbro to the shear/fault plane. The crystal plastic fabric often rotates through large angles into the shear zones. High temperature amphibole veins, sometimes cross-cutting, are common. The veins have a consistent dip and in some cases deflect the preexisting crystal plastic fabric. Moderately plunging fractures with slickenlines were also observed.
The petrophysics and paleomagnetics teams measured magnetic susceptibility, GRA density, and magnetic remanence of Cores 7R through 9R using core logging systems. The first set of subsamples was selected and cut from the working section halves of Cores 2R to 6R for the preparation of thin sections as well as shipboard chemical, paleomagnetic, and petrophysical analyses. Microbiology samples from Cores 6R to 9R were processed for full or partial suites of experiments, including culturing.
All scientists attended a talk on redox conditions and oceanic crust accretion.
Daily Science Report for 20 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 710.2 mbsl)
Science Update: At 0345 h we celebrated the recovery of the first core of Expedition 360, and by the end of the day we had recovered Cores U1473A-2R through 6R (9.5–51.3 mbsf) with a total recovery of 17.9 m (43%). Cores 2R–5R were described and consist of undeformed coarse-grained subophitic olivine gabbro with subordinate undeformed coarse-grained subophitic olivine-bearing gabbro, rare coarse-grained granular oxide-gabbro with plastic deformation, one intrusion of medium-grained granular gabbro, layers of fine-grained olivine-rich gabbro, and rare felsic vein intrusions. The intensity of alteration in Cores 2R and 3R was classified as slight to moderate. Cores 2R through 6R are highly fractured into pieces displaying crystal plastic fabric, which range from sub-horizontal to sub-vertical with a normal sense of shear. Many igneous contacts were observed, both magmatic and sheared, including a fine grained dike and one zone of grain size layering. The alteration veins are inclined and mostly amphibole and clay with the amphibole veins crosscutting the crystal plastic fabrics. A cataclasite and two fractures with slickenlines were noted.
The petrophysics and paleomagnetics teams measured magnetic susceptibility, GRA density, and magnetic remanence of Cores U1473A-2R through 6R. The microbiology team processed the first four samples from these cores for all or some of the tests proposed, including DNA, RNA, lipid frozen samples, samples for SEM, TC/TIC, ATP, exoenzymes, cell counts, and culturing. When drilling reached 50 mbsf they sampled drill fluids and surface seawater used for mixing with drill fluids.
The laboratory teams presented a summary of their findings at the Site 1105 review meeting. They also submitted their draft Site 1105 site reports and revised methods sections.
Daily Science Report for 19 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 708.2 mbsl)
Science Update: The day began with the recovery of the drill string, laying out the bottom-hole assembly (BHA) components on the rig floor, and flushing mud motor and underreamer with fresh water (0000–0500 h). The rotary core barrel (RCB) BHA was made up with a C-7 drill bit and lowered to 668 mbrf (0500–1215 h). Next we deployed the subsea camera system, picked up the top drive, and reentered Hole U1473A at 1535 h. At 1745 h, after recovering the camera system, the core barrel was dropped and cutting of the first Core U1473A-2R began. Coring advanced from 9.5 mbsf to 10 mbsf by midnight.
The microbiology laboratory team sampled surface seawater to test several protocols and made the final solutions for their experiments. Other laboratory teams worked on their Site 1105 reports. All scientists attended a talk on the onset of hydrothermalism in a gabbroic core complex.
Daily Science Report for 18 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 708.2 mbsl)
Science Update: The rig crew completed the 13.375 inch casing and mud motor stinger assembly, welded the casing and casing hanger together, and installed the hard rock skirt by 0130 h. They lowered the drill-in reentry system to 694 mbrf, picked up the top drive, and ran the subsea camera to the bottom of the pipe. The bit tagged the seafloor at 708.2 mbsl, and drilling in Hole U1473A began at 0535 h using the mud motor, tricone bit, and underreamer to open the hole for the drill-in casing. The signals from the two subsea cameras were lost at 1445 h and the camera was pulled to the surface. The broken part was replaced and the cameras redeployed by 1700 h. Drilling continued without the camera system except while handling the camera frame at the surface. We ended drilling with a mud sweep at 1845 h, after a period of no advancement, and left a 16.5 inch cased hole to 11.5 mbsf. A free-fall funnel was made up and dropped, and we observed its successful landing on the 13.375 inch casing hanger via subsea cameras from 1915 h to 2045 h. The stinger with bit, mud motor, and underreamer was released from the casing by pumping a release piston down the pipe and into the hydraulic releasing tool (HRT) and pulled clear of the reentry cone between 2045 h and 2230 h. The camera system was back at the surface by 2300 h and the crew prepared to recover the drill string.
The scientists worked on the Site 1105 report and attended a talk on mantle contribution in the oceanic crust.
Daily Science Report for 17 December 2015
Location: Hole U1473A (32°42.3622′S, 57°16.6880′E, 708.2 mbsl)
Science Update: The rig crew made up new 5 inch drill pipe and deployed it to 668 mbsl in preparation for a camera survey of the seafloor (~50 m radius) to find a suitably flat bare rock site for installing a drill-in reentry system. During the survey, the drill pipe and camera were raised and lowered by up to several meters as required by the seafloor morphology, and the selected location for Hole U1473A was at 708.2 mbsl. Total survey operations lasted from 0530–1530 h. Next, a 12.25 inch drill bit and a 11.75 inch mud motor with underreamer were assembled. The mud motor and retractable underreamer arms were tested at the moonpool, confirmed functional, and assembled with the hydraulic releasing tool (HRT). One joint of 13.375 inch casing was picked up, trimmed to 11.35 m length, and casing connections were tack-welded. The complete casing, HRT, mud motor, and running tool stinger assembly was readied for deployment.
We described and measured the final set of legacy cores from ODP Leg 179 (1105A-26R through 30R; 134.0–158.0 mbsf), which consist mostly of coarse grained subophitic olivine-bearing to olivine gabbro that are often orthopyroxene-bearing. Subordinate coarse grained granular oxide-bearing to oxide olivine gabbro was also observed. Intrusions of finer grained oxide-bearing olivine gabbro and numerous felsic vein intrusions are also present. The rocks are mostly fresh with zones of intense alteration usually occurring near veins. Frequent secondary minerals observed are amphibole, chlorite, secondary plagioclase, and brownish red clay. Both structural and intrusive contacts were observed with crystal plastic fabrics forming parallel and crosscutting contacts. Magmatic fabrics are weak and inclined. Alteration veins are inclined and composed of carbonate with open voids and amphibole. Several magmatic breccias, a brecciated fault zone, and semi-brittle fractures in pyroxene that are filled with plagioclase were observed. Paleomagnetists and petrophysics specialists completed their measurements of Hole 1105A sections. The new high-resolution (1 cm) record of magnetic susceptibility contact probe measurements acquired for Hole 1105A allowed us to test a filtering algorithm to remove spurious points from core data loggers.
Core description groups updated their working templates and description product specifications based on the redescription of the Site 1105 cores. A science meeting was held to clarify construction and use of alternate depth scales that adjust for stratigraphic overlaps associated with nominal core recoveries of >100% in Hole 1105A, which are also anticipated in future cores.
Daily Science Report for 16 December 2015
Location: Arrived at Site U1473 (proposed site AtBk-6) (32°42.34′S, 57°16.69′E)
Science Update: We completed the final 197 nmi of the 2817 nmi transit from Colombo to Site U1473 (proposed primary site AtBk-6) at an average speed of 11.6 kt and arrived at 1700 h. The rig crew began making up the hydraulic releasing tool (HRT) and the bottom-hole assembly (BHA), as well as picking up drill pipe from the riser hold hatch and drifting (checking) it. Bit depth below rig floor was 282 m at midnight. Earlier in the afternoon, senior ship, rig and science personnel met for a review and approval of the Site U1473 operations “pre-spud” plan.
We described and measured legacy Cores 179-1105A-20R through 25R (109.8–134.0 mbsf), which consist mostly of coarse grained granular olivine-bearing to olivine oxide gabbro, associated with small intercalations of coarse grained subophitic to poikilitic olivine-bearing to olivine gabbro. Fine grained gabbro crosscuts coarser grained gabbro. Very rare felsic veins were also described. Static background alteration intensity of these sections is slight to moderate. Amphibole and chlorite are the dominant alteration minerals. Crystal plastic fabric is abundant, forming decimeter thick zones of gneissic, oxide-rich bands with more discrete mylonitic zones. Throughout the interval several intensely fractured and altered fault zones occur along with several slickensides on fracture faces. Petrophysics specialists continued to measure point magnetic susceptibility and thermal conductivity, and paleomagnetists measured magnetic remanence after partial demagnetization on all sections.
An expedition science and objectives overview presentation was given to the ship’s crew and IODP technical staff. All scientists joined a seminar talk on fluids in the solid Earth.
Daily Science Report for 15 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (29°55.2′S, 59°15.8′E)
Science Update: We completed 265 nmi of transit at an average speed of 11.0 kt today, and 2620 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 at 1730 h tomorrow, 16 December.
We described and measured legacy Cores 179-1105A-13R through 19R (76.3–109.8 mbsf), which consist of coarse to medium grained gabbro and olivine gabbro, displaying a granular to subophitic texture associated with coarse grained granular oxide gabbro. Highly deformed areas of fine grained clinopyroxene-rich troctolite and rare felsic vein intrusions were also described. These cores show a low to moderate imprint of metamorphic alteration. So far, hundreds of alteration veins have been logged, indicating regimes of low-temperature veins formed under brittle conditions and inclined veins bearing mainly amphibole formed under high temperatures. Poorly developed magmatic and crystal plastic fabrics occur over broad tens of centimeter-thick intervals. Igneous contacts and fractured intervals are the most abundant structures, with vertical crystal plastic fabrics crosscut by oxide gabbro, and fine grained gabbro crosscutting coarse grained gabbro, and moderately to intensely fractured intervals accompanied by slickensides on fracture faces. Petrophysics specialists continued to measure point magnetic susceptibility and thermal conductivity, and paleomagnetists measured magnetic remanence after partial demagnetization on all sections.
Daily Science Report for 14 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (26°7.5′S, 61°52.2′E)
Science Update: We completed 256 nmi of transit at an average speed of 10.7 kt today, and 2355 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 at 2100 h on 16 December.
We described and measured legacy Cores 179-1105A-7R through 12R (47.8–76.3 mbsf), which consist mostly of coarse grained subophitic olivine oxide gabbros with minor intrusions of fine-grained granular Cpx-rich troctolite in the deepest sections. Numerous felsic vein intrusions were also described. These cores show low to moderate degrees of static metamorphic alteration. Alteration and felsic veins were particularly abundant and often inclined. Magmatic and crystal plastic fabrics occur in discrete intervals, but are not particularly well developed. Fractures are often inclined with some slickenlines present between broadly spaced zones of minor microfracturing in plagioclase and pyroxene.
Core describers began describing thin sections from Hole 1105A and preparing section and core summaries. Petrophysics specialists measured point magnetic susceptibility of all sections and thermal conductivity of a few selected pieces. Paleomagnetists partially demagnetized the sections and measured the magnetic remanence.
Daily Science Report for 13 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (22°34.7′S, 64°34.4′E)
Science Update: We completed 139 nmi of transit at an average speed of 5.8 kt today, and 2099 nmi of the total voyage of 2817 nmi. Between 0430–1715 h, the ship’s speed was reduced and the course changed to maneuver around the center of tropical depression Ex-Bohale. We now expect to arrive at Site U1473 at 2100 h on 16 December.
The science party described and measured the first 24 sections (15.0–46.7 mbsf) of the legacy cores from ODP Hole 179-1105A, along with the corresponding thin sections, sent to the ship from the Kochi Core Center before the start of the expedition. The interval consists mostly of olivine gabbro, numerous felsic vein intrusions, and minor oxide olivine gabbro. Most of the gabbro intervals display subophitic texture with a medium to coarse grain size. Alteration minerals are common and include amphibole, chlorite, serpentine, talc, clay minerals, and secondary plagioclase. Alteration and felsic veins have a variety of orientations along with an abundance of weakly to moderately developed magmatic fabrics. Crystal plastic fabrics were moderately developed and only in discrete 1–2 cm thick zones. Fractures were widely spaced, but some zones with abundant microfractures were present. Magnetic susceptibility was measured on suitable intervals using the contact probe. Paleomagnetists partially demagnetized the sections and measured the magnetic remanence, continuing the shipboard work from Leg 179.
Daily Science Report for 12 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (21°34.0′S, 67°27.5′E)
Science Update: We completed 267 nmi of transit at an average speed of 11.1 kt today, and 1960 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. Microbiology laboratory and downhole logging science and technical support teams held readiness review meetings with the Co-Chiefs and Staff Scientist. All laboratory groups submitted their method sections for the Expedition Reports. All scientists attended a presentation on the geophysical structure and development of oceanic core complexes.
Daily Science Report for 11 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (18°23.2′S, 70°43.4′E)
Science Update: We completed 280 nmi of transit at an average speed of 11.7 kt today, and 1693 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. Scientists continued to develop workflows and attended a science presentation on felsic rocks within the ocean crust. The entire ship’s crew held a ceremony to mark the crossing of the equator.
Daily Science Report for 10 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (14°50.5′S, 73°49.5′E)
Science Update: We completed 271 nmi of transit at an average speed of 11.3 kt today, and 1410 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. IODP personnel led two ship tours for the science participants who had not participated in the tours the previous day. Scientists kept exercising their laboratory procedures using cores from the 1987 ODP Leg 118 to Atlantis Bank. The science party attended a presentation on localization and deformation of Fe-Ti oxides in foliated and unfoliated rocks from ODP Hole 735B, Atlantis Bank.
Daily Science Report for 9 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (11°20.0′S, 76°51.2′E)
Science Update: We completed 279 nmi of transit at an average speed of 11.6 kt today, and 1142 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. IODP personnel led two ship tours for half of the science participants, and two more tours are scheduled for tomorrow. The core description scientists kept developing description templates while studying cores from the 1987 ODP Leg 118 to Atlantis Bank, which were laid out across the laboratory. Other laboratory groups practiced their procedures as well. All scientists attended a presentation on microbiology research in igneous basement.
Daily Science Report for 8 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (7°8.1′S, 78°17.8′E)
Science Update: We completed 275 nmi of transit at an average speed of 11.5 kt today, and 863 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. IODP personnel provided the scientists with more information on sampling procedures and depth computations. A science talk was presented on the tectonics and accretion of Atlantis Bank.
Daily Science Report for 7 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (2°35.0′S, 78°45.6′E)
Science Update: We completed 270 nmi of transit at an average speed of 10.8 kt today, and 588 nmi of the total voyage of 2817 nmi. We expect to arrive at Site U1473 on 16 December. At 0200 h, ship time was changed by −1 h to UTC + 4 h, which will be the time zone for the remainder of the cruise. At 0915 h we crossed the equator. A security drill was held at 1300 h. IODP staff provided the scientists with a hands-on introduction to the core description software, and the core description scientists submitted drafts of their template configurations. The scientists also received a presentation on the operations and engineering plans for Expedition 360.
Daily Science Report for 6 December 2015
Location: Underway to Site U1473 (proposed site AtBk-6) (1°53.2′N, 79°13.5′E)
Science Update: We completed 279 nmi of the total transit distance of 2817 nmi at an average speed of 11.4 kt, and we expect to arrive at Site U1473 on 16 December. The first lifeboat drill was held at 1030 h. The core description scientists received introductions to the microscopy and micro-imaging equipment and software. A science seminar talk was given on the results of prior explorations at Atlantis II Bank and SW Indian Ridge. At 1400 h, ship time was changed by −0.5 h to UTC + 5 h.
Daily Science Report for 5 December 2015
Location:
JCT Transfer Jetty, Colombo, Sri Lanka (6°56.50′N, 79°51.00′E)
Underway to Site U1473 (proposed site AtBk-6) (6°31.8′N, 79°41.9′E)
Science Update: Geochemistry, petrophysics, and paleomagnetism laboratory teams each reviewed and discussed their analytical and sampling plans for the cruise with the Co-Chiefs and Staff Scientist. The three core description laboratory teams continued discussing the detailed specifications for their template configurations. The science party received an overview presentation on ODP/IODP drilling in oceanic lithosphere. The remaining freight was loaded at a slow pace due to port logistical constraints. The pilot was on board at 2000 h and the last line was released at 2018 h, getting the ship underway to Site U1473 (proposed site AtBk-6) at full speed of 11.2 kt. We expect to arrive at Site U1473 on 16 December.
Daily Science Report for 4 December 2015
Location:
Unity Container Terminal Berth, Colombo, Sri Lanka (6°57.50′N, 79°51.30′E)
JCT Transfer Jetty, Colombo, Sri Lanka (6°56.50′N, 79°51.00′E)
Science Update: The scientists were introduced to the core description process, software, and data examples. The three core description laboratory teams then began discussing the detailed specifications for their template configurations. Loading and unloading of freight continued throughout the day. At the request of the port authority, the vessel was moved from the Unity Terminal Berth to the JCT Transfer Jetty between 2145 h and 2245 h. The vessel is scheduled to depart Colombo in the morning of 5 December as soon as the remaining freight is loaded.
Daily Science Report for 3 December 2015
Location: Unity Container Terminal Berth, Colombo, Sri Lanka (6°57.50′N, 79°51.30′E)
Science Update: The Expedition 360 scientists spent the day presenting and discussing their research proposals and sample requests. Loading and unloading of freight continued throughout the day. The vessel is scheduled to depart in the morning of 5 December.
Daily Science Report for 2 December 2015
Location: Unity Container Terminal Berth, Colombo, Sri Lanka (6°57.50′N, 79°51.30′E)
Science Update: Following a project overview by the EPM/Staff Scientist, the Co-Chief Scientists presented scientific background and objectives for Expedition 360. The operational approach was briefly presented and discussed as well. The four education and outreach team members then presented their background and objectives for the cruise. In the afternoon, the Captain and other senior ship crew personnel provided shipboard safety information. Loading and unloading of freight continued throughout the day. The vessel is scheduled to depart in the morning of 5 December.
Daily Science Report for 1 December 2015
Location: Unity Container Terminal Berth, Colombo, Sri Lanka (6°57.50′N, 79°51.30′E)
Science Update: All members of the scientific party, including scientists and education and outreach personnel, arrived on the ship and settled into their cabins before noon. The ship’s crew completed their crew change in the morning as well. In the afternoon, the science party members were introduced to each other as well as to technical support staff. They received presentations on living on the JOIDES Resolution and participated in laboratory safety tours. Port call activities continued, including loading and unloading of freight. The vessel is scheduled to depart in the morning of 5 December.
Daily Science Report for 30 November 2015
Location: Unity Container Terminal Berth, Colombo, Sri Lanka (6°57.50′N, 79°51.30′E)
Science Update: IODP SW Indian Ridge Lower Crust and Moho Expedition 360 officially began at 1100 h. The Co-Chief Scientists, Expedition Project Manager, and JRSO technical staff boarded the vessel and began port call activities, including meetings with the offgoing staff and discharging and receiving cargo. Expedition scientists are scheduled to board the ship on 1 December. The vessel is scheduled to depart in the morning of 5 December.