SIT09-P01

Japan Geoscience Union Meeting 2016

Mud gas monitoring for hard rock drilling*Takamitsu Sugihara1, Moe Kyaw Thu2, Kan Aoike1
1.CDEX/JAMSTEC, 2.ODS/JAMSTEC
Mud logging in a riser drilling operation has been powerful tool in the scientific drilling. Since
fast and safe drilling are minimum requirements in the deep drilling operation, it is generally
difficult that continuous coring is carried out to obtain geological sample (rocks and fluid).
Therefore, cuttings survey and mud gas monitoring in mud logging are essentially important in theriser drilling for scientific research. Some hard rock drilling operations by using the Chikyu havebeen planned (e.g., IBM, MoHole). Since continuous coring in the hard rock drilling is technicallymore difficult as compared with the drilling for sedimentary rocks and slow rate of penetration
results in consuming much of operation time, the cuttings survey is a unique approach forlithological characterization in the hard rock drilling. In addition, fluid sampling from hard rockcore is also difficult, even if core sample is obtained. Thus, the mud logging is especially
important for the hard rock drilling, not only minimizing operation time but also maximizing
scientific result. In this presentation, we will introduce current technology of advanced mud gas
monitoring and discuss on potential of the mud gas monitoring for the hard rock drilling.
Keywords: Mud logging, Hard rock drilling, Mud gas monitoring, Formation fluid©2016. Japan Geoscience Union. All Right Reserved.

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Japan Geoscience Union Meeting 2016

Preliminary result of the physical properties and downhole measurements during IODP Exp.
360 Indian Ridge Lower Crust and Moho
*Natsue Abe1, Benoit Ildefonse2, Donna K. Blackman3, Henry J.B. Dick4, Christopher J. MacLeod5,
Science Party IODP Exp.3606
1.R&D Center for Ocean Drilling Science Japan Agency for Marine-Earth Science and Technology,
2.Laboratorie Geosciences Montpellier, Universite Montpellier 2, 3.Scripps Institution of
Oceanography, University of California, San Diego, 4.Woods Hole Oceanography Institution,
5.Department of Earth Sciences, Cardiff University, 6.IODP
IODP Expedition 360 Phase I of the Nature of the Lower Crust and Moho at Slower Spreading Ridges(SloMo) project of a Multi-Leg Drilling Project was conducted drilling into the lower crustal
gabbroic rocks at Atlantis Bank, and penetrated from the top of ocean floor to 798.7 mbsf. The
cored interval is 742.7m and total recovered core length 469.65 m (63.2% recovery). Olivine gabbro
is the dominant lithology of the recovered core samples, followed in gabbro, oxide gabbro, andoxide-bearing gabbro. Lithological variation is small in the core samples. In order to understandthe petrophysics of the site, we measured physical properties on the whole round and splitted half
sections and, discrete samples and also took three runs of wire-line logging; Triple-combo, FMS and
UBI.
Phase II of the SloMo has proposed to drill 6 km through MOHO by the CHIKYU. In the meeting, we
would like to present the preliminary results, especially of the petrophysical measurements, of
IODP Expedition 360 and the future perspective leading to Phase II of the SloMo, a mantle drilling
into ultraslow-spreading ridges.
Keywords: IODP, Moho, SW Indian Ridge, Slow spreading ridge©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P02 -SIT09-P03

Japan Geoscience Union Meeting 2016

Peridotites outcroppted in the southern Mariana Trench*Shoma Oya1, Shigeki Uehara2, Katsuyoshi Michibayashi3, Yasuhiko OHARA4, Teruaki Ishii5, Kazutaka
Mannen6
1.Graduate School of Integrated Science and Technology,Shizuoka University, 2.Graduate School of
Science,Shizuoka University, 3.Institute of Geosciences,Shizuoka University, 4.Hydrographic andOceanographic Department of Japan, 5.Center for Integrated Research and Education of Natural
Hazards,Shizuoka University, 6.Hot Springs Research Institute of Kanagawa Prefecture
The Izu-Bonin-Mariana(IBM) arc, which is a typical oceanic arc, has 3000 km in length from thenorth to the south. The IBM forearc is non-accretionary convergent plate margin, where lithologies
outcropped on the land-side slope is similar to those found in many ophiolites. The Mariana trenchaxis forms an arc-like shape due to collision of Ogasawara plateau and Caroline ridge [1]. Thereby,
the southern Marianas from the south of Guam to Yap Trench junction shows characteristic morphology
where the trench axis runs across both Mariana volcanic arc and backarc basin (Mariana trough).
Geological expeditions in the southern Mariana Trench on the eastern side of the Challenger Deep
have found trench peridotites as shallow as 5800 m below the sea surface [2]. The petrologicalcompositions of these peridotites have both forearc-like depleted compositions and fertile
compositions similar to those reported in the northern Mariana trough [3]. In this study, we report
the geochemistry and fabric data for peridotites on the western side of Challenger Deep for the
first time since Hawkins and Batiza (1977) and attempt to present the full picture of mantle domain
outcropped in the southern Mariana trench.
We have selected about 140 samples from MARA20, MARA27 (dredged by R/V Thomas Washington during
MARIANA Expedition in 1978), KH98-1-D1, KH98-1-D2, KH98-1-D3 (dredged by R/V Hakuho during cruise
KH98-1 in 1998), KH03-3-D7, KH03-3-D8 (dredged by R/V Hakuho during cruise KH03-3 in 2003),
6K-1094, 6K-1095 (collected by R/V Yokosuka during cruise YK08-08 in 2008), 6K-1232, 6K1233, 6K1234(collected by R/V Yokosuka during cruise YK10-12 in 2010), 6K-1397,6K-1398 (collected by R/V
Yokosuka during cruise YK14-13 in 2014) and 6K-1429 (collected by R/V Yokosuka during cruise
YK15-11 in 2015).
Petrological compositions of peridotites from the western side of the Challenger Deep show
different characteristics between survey sites. Peridotites from the southwesternmost Mariana
forearc near the Yap Trench junction area (Site1:11°2’N139°3’E) have fertile compositions(Cr#=0.25-0.6) similar to those from the Parece Vela backarc basin [4], whereas peridotites fromthe other site close to Challenger Deep (Site2:11°1’N140°3’E) have depleted compositions(Cr#=0.6-0.9) similar to those from the northern Mariana forearc [5]. In our presentation, We willshow all chemical compositions of peridotites derived from the southern Mariana Trench in addition
to the data from the western side of the Challenger Deep obtained by this study.
REFERENCES[1] Miller et al., 2006, G3, 7, Q06012 [2] Michibayashi et al., 2009, G3, 10, Q05X06 [3] Ohara etal., 2002, Contrib mineral petrol, 143, 1–18.[4] Ohara et al.,2003, G3, 4(7), 8611 [5] Ishii etal.,1992, Proc. Ocean Drill. Program Sci. Results, 125, 445–487
Keywords: Trench Peridotite, Southern Mariana Trench, Geochemistry, Olivine Fabric©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P03 -SIT09-P04

Japan Geoscience Union Meeting 2016

Geochemical characteristics of Izu rear arc magmatism after the cessation of the Shikoku
Basin opening: Results from IODP Exp. 350*Tomoki Sato1, Takashi Miyazaki1, Yoshihiko Tamura1, Kenji Horie1, James B. Gill2, Ryoko Senda1,
Bogdan S. Vaglarov1, Qing CHANG1, Jun-Ichi Kimura1, Satoru Haraguchi1
1.Japan Agency for Marine-Earth Science and Technology, 2.University of California, Santa CruzInternational Ocean Discovery Program Expedition 350 Site U1437 drilled, for the first time, into
the rear arc volcaniclastic sediment in the Izu arc. The drilling reached 1806.5 m below seafloor(mbsf) and in-situ lava clasts were recovered in the deepest part of the hole (stratigraphic Unit
VII, below ~1460 m) (Tamura et al., 2015).
The U-Pb zircon ages obtained from an intrusive rhyolite sheet of the Unit VI at the depth of ~1390
mbsf showed 13.6+1.6/-1.7 Ma (Tamura et al., 2015) and 13.71±0.25 Ma, thus Unit VII lava clasts
suggest magmas erupted after the cessation of the Shikoku Basin opening (~15 Ma) and before onsetof the rear arc seamount chain magmatisms (hot fingers).
We have analyzed the major and trace element compositions, and Sr, Nd, Pb and Hf isotope ratios of
selected >2 cm lava clasts collected from Unit VII. These show neither rear arc nor Quaternary
volcanic front signatures in terms of trace elements and isotopes. The Nd and Hf isotope
compositions are similar to those in the Quaternary volcanic front magmas. However, most samples
have Sr and Pb isotope compositions similar with those in the rear arc magmas. The isotopes of Unit
VII are also similar to samples collected from the active rifts. Most of samples show low Ba/La and
La/Sm, and chondritic Sm/Hf ratios, suggesting that the addition of slab derived fluids/melts issmall despite the horizontal trend of Nd-Hf isotopes.
Above results show that Izu rear arc magmatism at Site U1437 differed from that in the rear arc
seamount chains after cessation of the Shikoku Basin opening. Contribution of the slab flux was
small and the source mantle was highly depleted in terms of isotopes.

©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P04 -SIT09-P05

Japan Geoscience Union Meeting 2016

Zircon U-Pb age and geochemistry of plutonic rocks in the Mineoka-Setogawa Belts:
Fragments of middle to lower crust of the IBM Arc?
*Yuji Ichiyama1, Hisatoshi Ito2, Natsumi Hokanishi3, Akihiro Tamura4, Shoji Arai4
1.Chiba University, 2.Central Research Institute of Electric Power Industry, 3.The University ofTokyo, 4.Kanazawa University
The Mineoka-Setogawa Belts are Paleogene accretionary complexes distributed around the Izu
Peninsula. These belts contain the various sizes of detrital and tectonic fragments ofserpentinized mantle peridotites, plutonic rocks (gabbro, diorite and tonalite), metamorphic rocks
and volcanic rocks (e.g., Arai 1994), which likely show ophiolitic constituents. Although Middle
Eocene microfossils were reported from sedimentary rocks in these belts (e.g., Saito, 1992;
Sugiyama and Shimokawa, 1990), reliable data of the isotopic age have not been obtained yet. In
this study, we determined the precise age of the plutonic rocks in the Mineoka-Setogawa Belts using
the zircon U-Pb method, and compared with the current age models proposed for the Philippine Sea
and IBM Arc.
The U-Pb age was measured from zircon grains collected from 10 samples of gabbros, diorites andtonalites using LA-ICP-MS (Thermo Fisher Scientific ELEMENT XR). The zircon U-Pb ages obtained fromall samples concentrate at approximately 35 Ma, regardless of the rock types. These ages are coeval
with the Eocene to Oligocene arc magmatism in the IBM Arc.
The whole-rock chemistry of the plutonic rocks from the Mineoka-Setogawa Belts shows calc-alkali
affinity and distinct negative anomalies of Nb and Ta in their trace element patterns, whichindicates that these plutonic rocks were formed by arc magmatism. Comparing the plutonic rocks withthe possible analogues of the IBM middle crust, the Tanzawa Plutonic Complex and the
Komahashi-Daini Seamount (Tamura et al., 2009), the major and trace elements of the plutonic rocks
from the Mineoka-Setogawa Belts are very similar to those of the Tanzawa Plutonic Complex and the
Komahashi-Daini Seamount.
The zircon U-Pb ages and geochemistry of the plutonic rocks in the Mineoka-Setogawa Belts probably
indicate that the ophiolitic fragments in the Mineoka-Setogawa Belts are derived from the crust andupper mantle of the IBM Arc. More thorough investigations of the ophiolitic fragments in the
Mineoka-Setogawa Belts will help us to understand the petrological evolution of the crust and upper
mantle beneath the IBM Arc.
Keywords: Mineoka-Setogawa Belts, Zircon U-Pb age, Plutonic rocks©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P05 -SIT09-P06

Japan Geoscience Union Meeting 2016

Estimate of the serpentinization process in the northern Fizh block, the Oman ophiolite*Yuki Yoshida1, Eiichi TAKAZAWA2, Hayato Ueda2, Yoshihiko Tamura3
1.Graduate school of science and technology, Niigata university, 2.Department of Geology, Facultyof Science, Niigata University, 3.R & D Center for Ocean Drilling Science, Japan Agency for
Marine-Earth Science and Technology
The mantle section of the Oman ophiolite is composed of partially-serpentinized harzburgite, dunite
and lherzolite. These peridotites are likely to have been suffered from hydrothermal circulation on
ocean floor because Oman ophiolite formed at mid-ocean ridge with fast spreading axis. In addition,
peridotites above the basal thrust may have reacted with a fluid liverated from metamorphic soleduring oceanic thrusting. Thus the study of serpentinization of the Oman peridotites is importantto understand fluid-peridotite reactions in the upper mantle. In this study, we examine
serpentinization processes in the Oman ophiolite on the basis of microscopic observation andchemical composition of serpentines in the northern Fizh mantle section. Lizardite is ubiquitously
present in the Fizh mantle section and develops typical mesh texture associated with lizardite
veins. Some clinopyroxenes are partially replaced by tremolite indicating possible fluid supply.
Because no antigolite has been found in the Fizh mantle section the reaction of clinopyroxene withhydrothermal fluid must have occurred at temperature between 600 and 900 degreeC. It suggests thatseawater can infiltrate the upper mantle at such high temperature beneath fast spreading mid-ocean
ridge.
One of the important observations in our study is that the peridotites in the basal part of the
mantle section contain abundant magnetites within the meshes and veins of serpentine. Moreover,some talc replaces the rim of orthopyroxenes. Previous studies proposed two-stage processes forserpentinization where magnetite formed at later stage. In addition, talc and forstelite can beproduced from enstatite and flluid at 650-750 degreeC (>6kbar). We consider that the fluid wasliberated from metamorphic sole and infiltrated the basal part of the mantle section during oceanic
thrusting.
On the other hand, in the peridotites inside the mantle section and near the Moho Transition Zone
no magnetite occur in meshed serpentine and only small amounts of magnetite occur in some veinsthat cut earlier meshed serpentine. The compositions of veined serpentines with magnetite arehigher in Si+Al and lower in Fe+Mg relative to meshed and veined serpentines without magnetite. It
is consistent with the model in which serpentine and magnetite formed from brucite under highsilica activity [Bach et al., 2006]. The Mg# [=Mg/[Mg+Fe] atomic ratio] of serpentines associatedwith magnetite in the basal peridotite are slightly lower than those of veined serpentines
associated with magnetite inside of the mantle section. This may indicate that Fe difussivity was
faster due to higher temperature during magnetite formation in the basal part of the mantle
section. Because the amount of serpentine is uniform inside the mantle section and has nocorrelation with the distance from the Moho Transition Zone lizardite formed at relatively low
temperature, probably less than 300 °C, by infiltration of surface water since obduction of theophiolite.
Keywords: Oman ophiolite, serpentinization, serpentine, lizardite, magnetite©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P06 -SIT09-P07

Japan Geoscience Union Meeting 2016

Geochemical evaluation of Haybi volcanic rocks as a protolith of amphibolites in themetamorphic sole of Oman ophiolite*Miyabi Sakashita1, Namiko Mori1, Eiichi TAKAZAWA2, Rikako Nohara2, Toshiro Takahashi2, Yoshihiko
Tamura3
1.Graduate School of Science & Technology, Niigata University, 2.Department of Geology, Faculty of
Science, Niigata University, 3.R & D Center for Ocean Drilling Science, Japan Agency for
Marine-Earth Science and Technology
We conducted geochemical analysis of the Haybi volcanics and amphibolites of metamorphic sole fromthe Sumeini Window in the northern Oman ophiolite to understand the protolith of amphibolites andtheir genetic relationship to the Haybi volcanics.
In the Sumeini Window the metamorphic sole consists of amphibolite, greenshist and quartzite. They
have been thermally metamorphosed during thrusting of ophiolite mantle section. The metamorphic
sole occurs tectonically above the Haybi Complex that includes metachart, limestone and volcanic
rocks so that the protolith of metamorphic sole is considered as Haybi Complex. Haybi volcanics arealternations of pillow lava and lava sheet. Some pillow lavas occur as blocks enclosed inmetachart.
By examination of whole rock compositions using discrimination diagrams and C1 chondrite-normalized
patterns of rare earth elements (REE) Haybi volcanics can be divided into either OIB or E-MORB
type. OIB-type basalts are pillow lava and lava sheet of alkali basalt to bsasanite and is
stratifically located beneath E-MORB type that is blocks of trachyandesite to dacite enclosed inmetachart. On the other hand, amphibolites can be divided into N-MORB to E-MORB type. Amphibolites
with E-MORB affinity are geochemically similar to E-MORB type volcanic rocks. There is no
systematic distribution of N- and E-MORB types along a wadi in the Sumaini Window. Both N- andE-MORB types occur near the contact between metamorphic sole and mantle section.
Whole rock Nd isotope ratio and La/Yb ratio show a broadly negative correlation that are similar
to those of volcanic rocks from Kerguelen islands. These variations can be explained by mixing
between MORB source mantle and isotopically enriched mantle associated with various degrees ofmelting. Our results show that N-MORB, E-MORB and OIB type volcanic rocks were distributed on theoceanic crust prior to the thrusting of Oman ophiolite. Then, N-MORB and E-MORB were subductedbeneath ophiolite so that they were metamorphosed to amphibolite by thermal metamorphism andaccreted to the base of the ophiolite. On the other hand, OIB-type volcanic rocks that are freefrom thermal metamorphism accreted beneath metamorphic sole after N-MORB and E-MORB at relatively
lower temperature and formed Haybi Complex.
Keywords: Oman ophiolite, metamorphic sole, Haybi volcanics, OIB, N-MORB, E-MORB©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P07 -SIT09-P08

Japan Geoscience Union Meeting 2016

Petrology and geochemistry of LREE-enriched fresh peridotite boulders from the basal partof the Fizh block, the northern Oman ophiolite*Satoko Ishimaru1, Shoji Arai2
1.Department of Earth and Environmental Science, Graduate School of Science and Technology,
Kumamoto University, 2.Department of Earth Sciences, Faculty of Science, Kanazawa University
Oman ophiolite, showing a great exposure (~ 500 km long), is one of the most famous ophiolites in
the world. Whole ophiolite sequence is well preserved and the emplacement age has been determined
as Cretaceous, based on the K/Ar dating on hornblendes from underlying metamorphic-sole amphibolite(e.g., Searle & Cox, 2002). There have been reported island-arc related volcanic rocks mainly inthe northern part of Oman ophiolite, and in the meanwhile, volcanic rocks comparable to typical
N-MORB are dominant in the southern part of the Oman ophiolite (e.g., Alabaster et al., 1982). It
is still debated that the Oman ophiolite is of mid-ocean ridge origin or of ridge axis on
supra-subduction zone origin. Recently, highly depleted harzburgites have been reported in thenorthern Oman ophiolite (Kanke & Takazawa, 2004); they were interpreted as products of thesecondary partial melting of residual harzburgites beneath the mid-ocean ridge, induced by H2
O-induced flux during detachment and intra-oceanic thrusting.
We found quite hard and fresh (LOI < 1.0) peridotite boulders at the southern basal zone of the
Fizh block (e.g., Wadi Hayl). The texture is variable (mylonitic, porphyroclastic, equigranular,
and coarse protogranular) and some porphyroclastic samples contain highly deformed fine-grainedzones. It is difficult to determine the modal proportion of minerals due to the presence offine-grained zone, but we can judge that they are mostly harzburgites and subordinatelylherzolites, based on petrography of coarse-grained part of the samples and their whole-rockmajor-element compositions (SiO2 = 43.5-46.4 wt.%, Al2O3 = 0.38-1.10 wt.%, and CaO = 0.49-1.68
wt.%). Chondrite-normalized (the values showing with subscript CN hereafter) whole-rock REE
concentrations show LREE-enriched U-shaped patterns, and the (La/Sm)CN and (La/Yb)CN are variable:
3.5-10.3 and 2.0-11.0, respectively. These values are quite high relative to the reported
harzburgites (0.02-0.11 and 0.44-0.70; Godard et al., 2000) and fertile lherzolite (0.09-0.11 and
0.04-0.06; Takazawa et al., 2001: 0.28-1.15 and 0.09-0.53; Khedr et al., 2014) from otherlocalities of the Oman ophiolite. The U-shaped REE pattern of ophiolitic peridotites has beeninterpreted as a result of secondary processes, such as serpentinization, ocean-floor alteration,or contamination of crustal materials during ophiolite obduction (Gruau et al., 1998). Low LOI
value (< 1.0) of our samples denies the contribution of serpentinization and alteration to theirenrichment of LREE, and indicates possible metasomatic addition of LREE to the mantle tectonite
during/before ophiolite obduction (at high-temperature stage).
Keywords: fresh peridotite, incompatible trace elements, mantle metasomatism, Oman ophiolite©2016. Japan Geoscience Union. All Right Reserved.

- SIT09-P08 -SIT09-P09

Japan Geoscience Union Meeting 2016

Evolutionary processes of submarine volcano in an incipient arc reference from the Oman
Ophiolite*Yuki Kusano1, Susumu Umino2, Keitaro Kitamura3, Kyoko Kanayama4
1.Geological Survey of Japan, 2.Department of Earth Sciences, Kanazawa University, 3.Asia Air
Survey Co., Ltd., 4.San'in Kaigan Global Geopark Promotion Office, Tottori Prefectural Government
The Oman ophiolite belonging to the Tethys ophiolite zone is one of the best places to investigate
magmatic and volcanic developing processes of an infant arc. The Ophiolite had formed on a
spreading axis and followed by subduction stage magmatism at approximately 100 Ma. The
volcanostratigraphy is similar to that of the Izu-Bonin-Mariana Arc (e.g. Starn, 2004). However,the latest U-Pb age of zircon in plutonic bodies shows that there is only 0.5 m.y. time gap between
the spreading and subduction stages (Riuox et al., 2014), therefore, it seems to record
short-spanned island arc magmatism. Progressive geochemical change from island arc tholeiite (LV2)
to boninite (UV2) in this period showed us the evolutionary process of the high-T and ephemeral
subduction zone (Kusano et al., 2015). To reveal the stress history during the subduction stage, wereconstructed accretionary process of the arc magmas at the northern Oman ophiolite.
The subduction stage volcanic rocks (V2) extend >350 km along the Oman Ophiolite. In Wadi Salahi
area, the V2 consist of the 600-970 m thick lower LV2 and 0-140 m thick upper UV2. Pahoehoe andsheet flows are dominate in the LV2, while 50 m thick pyroclastic rocks are partly distributed
upward. Plural flow units and sporadically distributed plugs and dikes at 1-3 km spaces arerecognized in the LV2. These plugs are 1.5-3 m in diameter with cylindrical layering offine-grained and coarse-grained parts. The distribution of plugs and dikes look unbiased in thestratigraphic horizon. Because the LV2 was erupted through cone sheets (Alabaster et al., 1982),
these plugs might be distributed along the “ring conduit”. Similar bulk rock compositions of the
LV2 including lava flows and pyroclastic rocks suggest the share in the magma chamber. However, E-W
concentration of strike of plugs and dikes would be resulted from the regional E-W compression(Umino et al., 1990).
Keywords: Subduction initiation, high-T subduction zone, Boninite, Oman Ophiolite, submarine
volcano geology©2016. Japan Geoscience Union. All Right Reserved.

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