Prof. Sugisaki performed a lot of creative studies dealing with various topics of earth science. We introduce his representative works in the following 6 sections: 1. Geochemical Studies of GroundWater, 2. Frontiers in Tectonochemistry, 3. Tectonic Behavior of Subsurface Fluids in Relation to Earthquakes, 4. Studies on Marine Sediments and Sedimentary Rocks, 5. Deep into “the Outback”—Prof. Sugisaki’s Pioneering Works on Archean Sedimentary Rocks, and 6. Study of Mantle Hydrocarbons as a Seed for Future Works.

Two different classifications for granitoids have been proposed independently in Australia (S-type and I-type) and in Japan (ilmenite-series and magnetite-series). The former classification is genetic and the latter is descriptive. We compared these classifications from a different chemical viewpoint: the feature of carbon-bearing gas species (methane, ethane, carbon dioxide) occluded in granitoids. These species were contained in mineral grains and grain boundaries and their composition might reflect environmental parameters at the crystallization of granitoids. We collected 315 granitoid samples from both classifications in Australia and Japan, and analyzed occluded gas by crushing these samples. Results indicated that magnetite-series granitoid samples generated under oxidized environmental conditions contained notably low carbon-bearing gas species; in particular, they contained no ethane. On the other hand, I-type granitoid samples were rich in carbon dioxide rather than methane compared with S-type samples. The identification of these qualitative features of carbon-bearing gas species of the S-/I-types and ilmenite-/magnetite-series correspond with data from previous work on the source rock of granitoids and the mineral assemblage of iron-oxide minerals. The carbon-bearing gas occluded in granitoids might be a useful conceptual tool for discussing the generation process and classification of granitoids.

Multivariate statistical analyses have been applied to a compositional data set for spring waters from the Arima and Kii areas in southwest Japan, for understanding sources and processes that produced the deep-seated Arima-type brine and the related spring waters in the areas. The data set consists of 14 rare earth elements (REEs), six major solute species (HCO₃, Cl, Na, Ca, K, Mg) and isotopic ratios of oxygen, hydrogen and helium (δD, δ¹⁸O, ³He/⁴He) from 19 sites. Independent Component Analysis (ICA) and k-means cluster analysis on the whitened data (KCA) are useful to extract independent features hidden in such a high-dimensional geochemical data set. As a result of ICA and KCA, four ICs and eight clusters were found to sufficiently and effectively describe the observed variability. Comparison of the results with δD, δ¹⁸O and ³He/⁴He provides geochemical interpretations on the extracted four ICs as follows: IC1 represents the overall REE concentration level; IC2 measures the amplitude of Eu anomaly inherited from local basement rocks/minerals; IC3 reflects the amplitude of (reversed) W-shaped pattern, which developed on mineral precipitation event(s) when the deep brine mixes with meteoric water in a relatively shallow aquifer under oxidative conditions, and IC4 measures the amplitude of Ce anomaly possibly by precipitation or mechanical filtering of CeO₂. Combination of the four ICs may create a complex and various REE pattern to explain the actual data. Although these geochemical features with Eu, Ce and W-shaped patterns have been broadly suggested to be important for understanding origin of the spring waters in the areas, this is the first time to demonstrate that the above features represent the independent processes and to compare them systematically with the regional compilation of the basement rock compositions. In addition, several clusters were found only in either the Arima area or the Kii area, which reflects broad geographical provenance of IC3 and IC4. These spatial variations can be attributed to compositional variations of the original deep brine, which possibly varies with slab depth and temperature to control the solute concentrations and subsequent geochemical evolution to produce different types of spring waters.

Rare Earth Elements (REEs) play an important role in interpretation of trace element behavior in geological systems. Changes in the shape of the normalized REE patterns measured from a suite of rocks can record fractionation or differentiation history of the magmatic source. In this paper, we report conjugate chondrite-normalized REE patterns from a felsic granulite in the Jirisan complex of southern Korea. Granulite bodies show systematic variation in REE patterns from north to the south. Rocks in the northern, middle and southern parts of the complex exhibit a range of REE patterns varying from weak, M-type tetrad patterns with a large, negative Eu anomaly to W-type patterns with a slightly positive Eu anomaly. Systematic variation in REE patterns supports a possibility for the interpretation of fractionation from granitic melts related to movement of metamorphic or magmatic fluids.

A granitic cobble was recovered with mud, semi-consolidated and consolidated siltstones to mudstones from the Dredge Site 16 (1,831 to 1,511 m below sea level) in the inner slope of Chile Trench at 47°48ʹ S during MR16-09 Leg 2 by the JAMSTEC R/V Mirai. Considering its occurrence and its sampling location at ca. 50 km far from coastline of the Chilean Patagonia province, the granitic cobble must be a dropstone. Obtained LA-ICPMS ²³⁸U-²⁰⁶Pb age for the essential zircon crystals was 79.7 ± 1.0 Ma (2σ) on the basis of unmix age function. According to the previous researches, such granitic plutons having ca. 80 Ma occurs limitedly in Fjord Baker area (48°S) in the northern part and along the Magellan Strait (52°S) in the southern part of South Patagonian Batholith. Our results of U-Pb age as well as the rock description provide constraint for provenance of the granitic dropstone to be transported from the Fjord Baker area into the deep sea by an iceberg when glaciers widely covered high plateaus of the Chilean Patagonia province were melted after the last glacial maximum.

The Cretaceous to early Paleogene magmatism occurred in the Honshu Arc actively and the formation age for this period shifted regionally in the Southwestern and Northeastern Japan Arcs, respectively. The Tadamigawa older-stage granites are located to the west of the Tanakura Tectonic Line (TTL), which is the boundary of the Northeastern Japan Arcs and the Ashio belt, and the formation age and source of the Tadamigawa older-stage granites were unclear. In this study, we determined the formation age of the Tadamigwa older-stage granites by zircon U-Pb and whole-rock and mineral Rb-Sr datings and estimated the origin of the granites by the initial Sr isotopic ratio. The Tadamigawa older-stage granites have two intrusion ages, 107–93 Ma and ca. 62 Ma. In addition, the older granites show +4.6ε_Sr – +20.4ε_Sr, and the younger granites show +64.0ε_Sr. The Tadamigawa older-stage granites to the west of the TTL of northeastern Japan comprise two types of plutons with different ages and origins.

Various granitoid bodies from the Neoproterozoic to Late Cenozoic intruded in the Sanandaj-Sirjan zone (SaSZ) in western Iran. In this research, we have compiled data for rare earth elements (REEs) concentration in the granitoid bodies which we have collected in the northern part of the SaSZ in this decade. The abundances of ∑REEs in a part of the granitoids are over 500 and even 2000 ppm. Although most of the granitoids such as Ebrahim Atar, Panjeh, Ghorveh, Kangareh, and Ghalaylan have low or normal values of ∑REEs and are not hopeful for future exploration, some hopeful bodies such as the Mobarak Abad granitoid in the east of Sanandaj and the Hassansalaran A-type granites in the east of Saqqez are recognized as REEs potential for future exploration. The chemical compositions of the REEs-enriched granites such as the Hassansalaran A-type and Mobarak Abad granites infer that the granites were generated in an extensional tectonic regime. Our finding shows that the granitic rocks which are related to the within plate tectonic setting in the SaSZ, NW Iran, can be considered as good potential for REEs exploration in the future.

Spherical carbonate concretions are commonly observed in marine clayey sedimentary strata and often contain well preserved fossils. Previous studies revealed that the spherical concretions are formed by the very rapid reaction with decomposed organic matter from inside and Ca²⁺ ion of seawater. However, the detailed mass transport process during concretion formation has not been completely understood. Here two different size of spherical concretions, cm size of tusk-shell concretions and metre size of Moeraki boulders, are re-examined to understand the diffusion oriented formation process. Field observations, and detailed mineralogical (XRD) and geochemical analyses (SXAM, XRF, δ¹³C) revealed diffusive transport of HCO₃⁻ from decaying organic matter and Ca²⁺ from surrounding pore-water of marine origin led to solid carbonate precipitation reactions that progressed from the margin of a concretion. Based on the compositional gradients across the concretions, a diffusion based diagram has been applied to estimate the growth rates of the different size of spherical concretions. The process and rate estimation indicate that even gigantic spherical concretions can form quite rapidly in the muddy matrices under a diffusion-controlled transport regime.

To better understand the activities of subsurface microbes producing and oxidizing methane in terrestrial regions and the hydrological factors controlling the activities, we conducted geochemical and microbiological studies on the Holocene mud beneath the Kanto Plain. The ¹³C- and ¹⁴C-tracer experiments indicates that the methane oxidation activity far exceeded the methane production activity in the sediments, which is consistent with the predominance of anaerobic methane-oxidizing archaea (ANME)-1 in the archaeal population. Depth profiles of sulfate and sulfide ions in the pore water and the hydrogen and oxygen isotopic compositions of the pore water in the sediments indicates that surface meteoric water had recently infiltrated into the muddy sediments and a reduction of the sulfate derived from the meteoric water had occurred in the upper part of the sediments. Meanwhile, the molar ratios of methane to ethane plus propane and the carbon isotopic compositions of methane showed that methane in the Holocene mud was microbial in origin. Because the methane was dissolved in the low-salinity pore water, which had almost completely replaced the original paleo-seawater, the methane production activity would have occurred after the replacement. The pore water in the lower part of the sediments with low hydrogen isotopic compositions may have been derived from waters recharged under colder climate, such as the Last Glacial Maximum. The small size of the pores in the muddy sediments restricts the flow and migration of microbes. The carbon isotopic relationship between archaeal lipids and dissolved carbon dioxide fits the isotopic fractionation associated with carbon fixation and lipid biosynthesis by methane-producing archaea rather than that by methane-oxidizing archaea, which suggests that the dominant ANME-1 may have produced the dissolved methane under a low sulfate condition before the infiltration of meteoric water into the sediments.

To reveal the thermal history of the Allende (CV3) meteorite, we pyrolyzed insoluble organic matter (IOM) from the meteorite and examined the chemical and isotopic composition of the pyrolysates against the pyrolysis temperature. Major pyrolysates from the Allende IOM were sulfur (S)-bearing compounds (H₂S, SO₂, CS₂, and OCS), oxygen (O)-bearing compounds (H₂O, CO, and CO₂), and hydrogen gas. S-bearing compounds mainly appeared in a pyrolysis temperature range of 250–300°C, O-bearing compounds mainly appeared at all pyrolysis temperatures, and hydrogen gas mainly appeared in a range of 550–800°C. The IOM scarcely released aliphatic and aromatic hydrocarbons and nitrogen (N)-bearing compounds, although they were major pyrolysates of the Murchison IOM at 450–550°C. Regarding the calculated isotopic data of the Allende pyrolysates, the δ¹³C value was almost constant for all the pyrolysis temperatures. The δ¹⁵N value was constant up to 550°C and then drastically decreased at 550–800°C. The δD values of the pyrolysates at all pyrolysis temperatures were lower than the δD values of the starting IOM. If we assumed that the Allende IOM originated from a primitive IOM (such as the Murchison IOM), our results suggested that the Allende IOM suffered a two-stage thermal process: the first stage was a thermal event below 550–800°C that caused the loss of primary materials (aliphatic and aromatic hydrocarbons, N-bearing compounds) enriched in ¹³C, D and ¹⁵N, and the second stage was a thermal event below 300°C that led to the addition of secondary S- and O-bearing compounds depleted in D. Based on our data and previously reported data (the peak metamorphic temperature of the Allende IOM is 550–590°C), it was proposed that the Allende meteorite experienced thermal metamorphism at 550–590°C followed by an alteration below 300°C.

Ulaanbaatar, the capital city of Mongolia, is subjected to heavy atmospheric pollution especially in winter. In order to clarify inorganic and organic chemical characteristics of suspended particulate matters (SPMs) and contribution degrees of SPM sources throughout the year, 53 SPM samples collected during January 2014 to April 2015 at central part of Ulaanbaatar were analyzed for total carbon, total hydrogen, water soluble cations and anions, metal elements, and aliphatic and polycyclic aromatic hydrocarbons (n-alkanes and PAHs, respectively). The SPMs collected in the cold season (November to March) show high concentrations of many chemical species, such as total carbon and hydrogen, water soluble ions, n-alkanes and PAHs. The SPMs in the cold season are concluded to be harmful for human health, because of high concentrations of carcinogenic As and PAHs up to 45 and 8.8~13 ng/m³, respectively. Principal component analysis of chemical species suggests that SPMs in Ulaanbaatar can be explained mostly by 2 components; coal and biomass combustion (about 70%) and soil dusts (about 15%). However, we could not quantitatively discriminate the contribution degrees of coal burning at thermal power plants and coal and biomass burning at households in the Ger (traditional Mongolian dwelling houses) area. Direct analyses of carbonaceous ashes adhering to tunnels of power plants and Ger houses must be indispensable for determination of contribution degrees of these sources.