熊谷 英憲

Abstract The Martian atmospheric Ne may reflect recent gas supply from its mantle via volcanic degassing, due to its short (∼100 Myr) escape timescale. The isotopic ratio of the Martian atmospheric Ne would therefore provide insights into that of the Martian mantle, further suggesting the origin of Mars volatiles during planetary formation. Mass spectrometric analysis of the Martian atmospheric Ne, however, has faced challenges from interference between ²⁰Ne⁺ and ⁴⁰Ar⁺⁺. Previous studies using a polyimide membrane for ²⁰Ne/⁴⁰Ar separation were limited by the drawbacks of elastomeric O-rings to support the membrane, such as low-temperature intolerance, outgassing, and the need to endure environmental conditions during the launch and before/after landing on Mars. This study proposes a new method employing a metal C-ring to secure a 100 μm polyimide sheet within vacuum flanges. Environmental tests, including vibration, shock, extreme temperatures, and radiation exposure, were conducted on the gas separation flanges. Pre- and post-test analyses for He, Ne, and Ar demonstrated the membrane-flange system’s resilience. Gas permeation measurements using terrestrial air effectively permeated ⁴He and ²⁰Ne, while reducing ⁴⁰Ar by more than six orders of magnitude. This study achieved a <3% accuracy in determining the ²⁰Ne/²²Ne ratio, sufficient for assessing the origins of Ne in the Martian mantle. Furthermore, experiments with a 590 Pa gas mixture simulating the Martian atmosphere achieved a 10% accuracy for the ²⁰Ne/²²Ne isotope ratio, with gas abundances consistent with numerical predictions based on individual partial pressures. These results validate the suitability of the developed polyimide membrane assembly for in situ Martian Ne analyses.

地質試料に対する希ガス同位体分析は、大気混染との戦いである。一方、今世紀に入っての二次イオン質量分析計(SIMS)やレーザーアブレーション誘導結合プラズマ質量分析計(LA-ICP-MS)などの局所同位体分析の発展は地球史初期の様相をはじめ地質試料から多様な情報を引き出しつつある。熱年代学にも活用されている希ガス同位体分析がこの流れにどの程度追随できるかは予断を許さない。この小論では、一世代前の希ガス質量分析装置を用いた筆者らの局所微量分析の試みを報告する。

As the alternate survey protocol for AUV-ROV sequential focused geological survey in great water depth, HOV mounted MBES survey followed by the geological observation and sampling was conducted. HOV mounted MBES provided a sub-meter scale high resolution bathymetric map, which efficiently supported the geological observation and resolve down to one meter scale morphological features successfully. Further, a pre-gridded point clouds imagery contains detailed morphological information.

<title>Abstract</title>Seafloor massive sulphide (SMS) deposits, modern analogues of volcanogenic massive sulphide (VMS) deposits on land, represent future resources of base and precious metals. Studies of VMS deposits have proposed two emplacement mechanisms for SMS deposits: exhalative deposition on the seafloor and mineral and void space replacement beneath the seafloor. The details of the latter mechanism are poorly characterised in detail, despite its potentially significant role in global metal cycling throughout Earth’s history, because in-situ studies require costly drilling campaigns to sample SMS deposits. Here, we interpret petrographic, geochemical and geophysical data from drill holes in a modern SMS deposit and demonstrate that it formed via subseafloor replacement of pumice. Samples from the sulphide body and overlying sediment at the Hakurei Site, Izena Hole, middle Okinawa Trough indicate that sulphides initially formed as aggregates of framboidal pyrite and matured into colloform and euhedral pyrite, which were replaced by chalcopyrite, sphalerite and galena. The initial framboidal pyrite is closely associated with altered material derived from pumice, and alternating layers of pumiceous and hemipelagic sediments functioned as a factory of sulphide mineralisation. We infer that anhydrite-rich layers within the hemipelagic sediment forced hydrothermal fluids to flow laterally, controlling precipitation of a sulphide body extending hundreds of meters.

We recovered sedimentary and plutonic rocks from the off-ridge portion of the Southwest Indian Ridge (37 degrees 00.02' E, 44 degrees 49.73' 5, 2165 m deep). The petrography, geochemistry, and geochronology of these plutonic rocks were analyzed. Ar-Ar dating of biotite in the plutonic rocks yielded early Paleozoic ages of approximately 475 and 490 Ma, indicating that these rocks are likely related to Antarctic orogenies during the late Neo-proterozoic to early Paleozoic. In addition, the samples exhibited trace element compositions and low initial epsilon Nd values (-8 and -12) similar to those of rocks from western Dronning Maud Land and the Transantarctic Mountains, Antarctica. Such similarities suggest that these plutonic rocks from the off-ridge portion of the Southwest Indian ridge were derived from western Dronning Maud Land or the Transantarctic Mountains and deposited by melting icebergs as dropstones.

Although seafloor massive sulfide (SMS) deposits are crucially important metal resources that contain high-grade metals such as copper, lead, and zinc, their internal structures and generation mechanisms remain unclear. This study obtained detailed near-seafloor images of electrical resistivity in a hydrothermal field off Okinawa, southwestern Japan, using deep-towed marine electrical resistivity tomography. The image clarified a semi-layered resistivity structure, interpreted as SMS deposits exposed on the seafloor, and another deep-seated SMS layer at about 40-m depth below the seafloor. The images reinforce our inference of a new mechanism of SMS evolution: Upwelling hydrothermal fluid is trapped under less-permeable cap rock. The deeper embedded SMS accumulates there. Then hydrothermal fluids expelled on the seafloor form exposed SMS deposits.

Natural gamma ray logging was carried out at the five wells in Izena Hole off-shore Okinawa by D/V Chikyu on November to December in 2016. This is one of the research cruise under an umbrella of Cross-ministerial Strategic Innovation Promotion Program (SIP), "Next-generation technology for ocean resources exploration (Zipangu in the Ocean program)". The purpose of this survey is to understand geological profile and distribution of the subsurface hydrothermal deposit. It is difficult to take good quality and recovery cores in hydrothermal brittle formation. On the other hand, the continuous natural gamma ray logging data allows us to describe continuous vertical formation profile. The memory-type logging tool was stuck out just below the drill bit at the bottom of borehole after cutting cores. The tool measures logging data during pulling out of the hole. Natural gamma ray, temperature and pressure were measured in the boreholes. The gamma ray data by logging tool has good correlation with that in the core data by laboratory measurement until ~30-80m below sea floor at the good core recovery intervals. The logging data are only continuous profile below the depth till maximum 180m below sea floor. The gamma ray data indicate classification of sediment layer, ore body, and alternate layer in this region. The temperature logging indicates potential of hydrothermal deposit activity. The pressure data shows static water column.

© 2016 JFES. All rights reserved. The CK16-01/Expedition 908 was conducted at the active hydrothermal field in the Iheya-North Knoll and Noho in Okinawa trough Japan by D/V Chikyu in Feb-Mar 2016. This expedition drilled hydrothermal fields recently discovered in the Iheya Small Ridge (Noho site: as reported in the JOGMEC news release on December 4, 2014) using LWD and geothermal tools. The purpose of this study in 2016 are to establish the origin and development model of deep water hydrothermal deposit, and to examine continuity of reservoir and mineral deposits in this area. The project was a part of “Scientific Research on Genesis of Marine Resources” for “Next-generation Technology for Ocean Resources Exploration,” of the Cross-ministerial Strategic Innovation Promotion Program (SIP). LWD was conducted at 3 sites in Iheya-North Knoll and at 4 site in Noho. The gamma ray, various resistivities, and high resolution resistivity borehole image allows us to understand the futures of hydrothermal sediments. Real-time annular pressure and temperature allow us to analyze dynamic thermal formation fluid flow. The cores were acquired and quick measurement and analysis were carried out by onboard scientists. Monitoring devices were successfully installed at active hydrothermal field in Iheya and Noho to record temperature, pressure and flow rate of the hot fluid, and to observe its process of deposits.

© 2015 JFES. All rights reserved. The CK14-04/Expedition 907 was conducted at the active hydrothermal field on the Iheya-North Knoll at Okinawa trough Japan by D/V Chikyu in July 2014. High temperature hydrothermal fluid flow exceeding 300degC was expected at the active hydrothermal deposits from the previous surveys. To achieve successful survey and to protect LWD tools, 1) pre-survey dynamic temperature modeling was carried out, 2) continuous circulation system "Non Stop Driller", which makes constant drilling fluid circulation even during pipe connection, was used, 3) LWD tools were upgraded up to 175degC, was used, and 4) real-time annular temperature and pressure were monitored. Flow rate was carefully controlled with the Non Stop Driller System after the pre-survey temperature modeling. The six wells were drilled with LWD successfully. The water depths are 886m to 1132m. High quality natural gamma-ray and resistivity, annular temperature and annular pressure mounted on arcVISION and TeleScope throw a light to active hydrothermal deposits first ever. The maximum annular temperate anomaly at 84degC was observed. The combination of natural gamma-ray and resistivity logs, and time series of annular temperature and pressure allows us innovative interpretation for deep water hydrothermal deposits. These results suggest that a LWD survey can be a new method for investigating sea-floor hydrothermal deposits.

Kumagai, H, Adrovic, F, Iwase, R, Kinoshita, M, Machiyama, H, Hattori, M &amp; Okano, M, 2012, , InTech.

Kumagai, H, Tsukioka, S, Yamamoto, H, Tsuji, T, Shitashima, K, Asada, M, Yamamoto, F &amp;amp; Kinoshita, M, 2010, &#039;Hydrothermal plumes imaged by high-resolution side-scan sonar on a cruising AUV,Urashima&#039;, vol. 11, no. 12.

&amp;emsp;As our understanding of seafloor hydrothermal systems grows, we recognize they are not always stable and sometimes show dramatic changes. In this review, the authors present a compilation of geochemical and geochronological studies that are helpful when investigating the evolving processes of submarine hydrothermal systems.&lt;br&gt;&amp;emsp;Chapter II describes the systematics and methodology of three dating techniques with discussions on their application to minerals formed by seafloor hydrothermal activities. The K-Ar (Ar-Ar) technique is popular for dating igneous rocks, but it is not appropriate for dating hydrothermal minerals because potassium is a trace component of sulfide/sulfate minerals. Following recent progress, micro-analytical techniques applying laser fusion are applicable for dating fluid inclusions and/or hydrothermal alteration minerals, which could provide important geochronological information. Uranium and thorium series disequilibrium dating have been employed for previous geochronological studies of hydrothermal minerals obtained from submarine ore deposits. To cover a wide time range, it is necessary to use various combinations of parent and daughter nuclides. Applying ESR dating to hydrothermal minerals is a rather new challenge. Although it needs several investigations to establish the methodology, it could be a useful rapid dating technique for a time range of less than one thousand years.&lt;br&gt;&amp;emsp;Chapter III introduces studies focusing on the evolution of seafloor hydrothermal activities over a short time scale (one week to a few years). Detection of event plumes associated with seafloor lava eruption brought an awareness of episodic hydrothermal activity triggered by magmatic perturbation. Subsequent dive studies revealed evolving geochemical processes, such as major changes of volatiles and elemental species concentrations of venting fluid. With remote real-time monitoring of acoustic T-waves generated by seafloor seismic activities, event detection and response cruises have been conducted successfully to investigate various evolving processes in more detail.&lt;br&gt;&amp;emsp;Chapter IV introduces studies focusing on the evolution of seafloor hydrothermal activities over a long time scale (tens of thousands of years). Radiometric dating studies of hydrothermal minerals such as sulfide and manganese oxide collected from the TAG mound, which is one of the largest hydrothermal mound structures, reveal an age distribution over at least 15000 years separated by quiescent intervals lasting up to 2000 years. On slow spreading ridges such as the Mid-Atlantic ridge, major fracture systems focus the hydrothermal discharge at one place for more than one thousand years with repeated reactivation.&lt;br&gt;&amp;emsp;In Chapter V, the authors discuss the direction of future studies. Although hydrothermal systems on mid-oceanic ridges have been well studied, those related to arc-backarc magmatic activities could provide more appropriate fields for studying the evolutionary process of submarine hydrothermal systems. Combining geochronological studies with geochemical and mineralogical studies would be important for reconstructing the evolution process in more detail.

Frictional melting experiments were performed on fine grain homogeneous gabbroid with high temperatures induced by frictional heating using a high-velocity apparatus. We examined whether rapid fault movement can equilibrate fault rock gas with atmospheric components by measuring volatile gas and noble gas isotopes from a gabbroid sample using a quadrupole mass spectrometer to detect released gas from the simulated fault rock.The anticipated rapid equilibration of volatiles during the frictional melting of rocks implies that the noble gas and volatile were released and mixed with the atmosphere during this experiment. Gases released from the sample were collected in a small aluminum tube in nitrogen atmosphere before and after the frictional melting experiment. The gas comprised carbon dioxide, water vapor, hydrogen, helium, and other noble gases. The He/Ar ratio and H2 concentration are higher than the pre-analysis of N2 atmosphere. This release of volatiles is consistent with the pseudotachylyte-like post experimental texture of specimen. It is also consistent with the co-seismic geochemical anomaly observed along a natural fault system.