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Dating the arrival of the first hominins in Java The World Heritage archaeological site at Sangiran on the island of Java in Indonesia has major importance for the understanding of human arrival and evolution in Asia. However, the timing of the first appearance of Homo erectus at the site has been controversial. Using a combination of dating techniques for hominin-bearing sediments, Matsu'ura et al. resolved the arrival of H. erectus at ∼1.3 million years ago (see the Perspective by Brasseur). This dating suggests that the earliest hominins in Sangiran are at least 200,000 years younger than has been thought and may represent an important step to the resolution of the controversy. Science , this issue p. 210 ; see also p. 147

Isotopic analysis of Fe has proved to be a productive tool for the study of the formation and evolution of planetary bodies. The Fe isotopic studies on the Moon revealed that low-Ti and high-Ti basalts are positively correlated with TiO2 contents, indicating the occurrence of Fe isotopic fractionation during lunar magma ocean differentiation (Weyer et al., 2005; Liu et al., 2010; Wang et al., 2015; Sossi and Moynier, 2017 ). If true, very low-Ti basalts may be more representative of the lunar mantle than high-Ti and low-Ti basalts. Thus, an Fe isotopic study of very low-Ti basalts is required to investigate the Fe isotopic evolution scenario during lunar magma ocean differentiation. In this study, we measured Fe isotopic ratios of soil samples from the Soviet Luna missions, Luna 16, 20, and 24, using MC-ICP-MS. Bulk soil samples without isolation of components and separated monomineralic grains (olivine, pyroxene, and agglutinate) were dedicated for the Fe isotopic study. Among our samples, Luna 24 soil is recognized as very low-Ti basalt. Evidence of non-mass-dependent Fe isotopic fractionation was not found in bulk soils and separated monomineralic olivine, pyroxene, and agglutinate grains. Lunar regolith samples are weathered by meteorite impacts on the Moon’s surface. A mature regolith sample, L1613, showed clearly distinguished Fe isotopic compositions between the fine-grained fraction (δ57Fe = 0.54 ± 0.06‰) and the coarse-grained fraction (δ57Fe = 0.20 ± 0.06‰). Such Fe isotopic differences among different size fractions were smaller in the submature sample (L2001) and the immature sample (L24130.3). The Fe isotopic ratios of separated grains show that agglutinates have higher δ57Fe values than bulk and monomineralic grains, indicating abundant nanophase Fe in agglutinates and partial evaporation of Fe during its melting. The δ57Fe value for the coarsest-grained fraction of L24130.3 was found to be 0.08 ± 0.04‰, which is the first Fe isotopic composition reported for lunar samples with very low-Ti mare basalt composition. This value is clearly lower than previously reported δ57Fe values for high-Ti and low-Ti basalts and is nearly identical to those of Mg-suite rocks. This observation is consistent with the Fe isotopic evolution model during lunar magma ocean differentiation ( Sossi and Moynier, 2017 ). Our results related to very low-Ti basalt showed that the bulk silicate Moon has lower Fe isotopic composition than the value estimated from averaged low-Ti or high-Ti basalts. Given the data known to date, including our results, we conclude that it is most likely that Earth and the Moon have the same Fe isotopic composition. We believe that isotopically heavy Fe of silicate Earth is balanced by isotopically light Fe of Earth’s core, as suggested by Galimov’s (2011) model for the formation of the Earth-Moon system.

The Oeyama ophiolite unit is one of the oldest components of the subduction orogenic belts in the Japanese Islands and is important for understanding the initiation of plate subduction in the proto-Japan region. This study performed U–Pb and Lu–Hf isotopic and trace element analyses of zircon in gabbroic rocks from the Oeyama mafic–ultramafic complex, the type locality of the Oeyama ophiolite unit. This study obtained a weighted average zircon 206Pb/238U age of 544 ± 4 Ma, which indicates an igneous age of the gabbroic rock. Trace element analysis of the zircons revealed that the host rock was derived from the mantle depleted of incompatible elements such as the depleted mid-oceanic ridge mantle. The present igneous age and geochemical features of the zircons are consistent with previous work for other parts of the Oeyama ophiolitic unit. The isotopic signature of Hf also indicated that the gabbroic rock was derived from the depleted mantle domain. The Hf isotopic signature is more depleted than those represented by zircons in the jadeitite associated with the Oeyama ophiolite unit. These results demonstrated that the older crustal material was involved in the initial oceanic plate subduction along the proto-Japan arc.

The Kuroshio Large Meander (LM) is known to be highly aperiodic and can last from 1 to 10 years. Since a stationary cold core formed between the Kuroshio and the southern coast of Japan off Enshu-Nada and approaching warm saltier water on the eastern side of the LM changes the local environment drastically, many commercially valuable fish species distribute differently from the non-LM period, impacting local fisheries. Despite this importance of the LM, the influences of the LM on the low trophic levels such as phytoplankton and zooplankton have still been unclear. In this study, satellite daily sea surface chlorophyll data are analyzed in relation to the LM. The results show positive anomalies of the chlorophyll-a concentration along the Kuroshio path during the LM periods, 2004–2005 and 2017–2019, from the upstream off Shikoku to the downstream (140°E). These positive anomalies are started by the triggering meander generated off south of Kyushu, which then slowly propagates to the downstream LM region in both the LM periods. Even though the detailed patterns along the Kuroshio region in the two LM periods were different, similar formations of the positive anomalies on the western side of the LM with shallower mixed layer depth are observed. Furthermore, we found clear relationships between the minimum distance from several stations along the coast to the Kuroshio axis and the mean chlorophyll-a anomaly, with significant correlations with the distance from different stations.

This study presents position-by-position $t-T$ paths within a granitic pluton based on thermochronological data, and describes their constraints and their relationship with fracture frequency, as an example from the Toki granite, central Japan. The cooling paths have position-specific characteristics; a single $t-T$ path does not represent the cooling behavior of the entire pluton. Such position-specific $t-T$ paths enable us to evaluate three-dimensional thermal evolution within the granitic pluton, and thus can clarify the detailed formation history of the entire pluton after the incipient intrusion of the granitic magma into the shallow crust. This study reveals the relationship between position-specific $t-T$ paths and fracture frequency, and thus provides a criterion for evaluating the fracture population in terms of thermal stress., 本研究は、中部日本に位置する土岐花崗岩体を研究対象とし、熱年代学的な手法で冷却履歴(温度-時間履歴)を取得した。10本のボーリングコアから採取された15試料に対して、ジルコンU-Pb年代,黒雲母K-Ar年代,ジルコンフィッション・トラック(FT)年代,アパタイトFT年代、およびFTデータの逆解析からなる温度-時間履歴を提示した。得られた岩体内部の複数地点の冷却履歴の相違を比較し、その位置的な相違を生む原因について言及した。これは熱進化モデルの構築に資するデータとなる。また花崗岩内における物質移動は、水みちとして機能する割れ目により大きく支配されることから、割れ目の分布特性と得られた温度-時間履歴の関連について検討を行った。

The 11th Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 2 Dec.

Platinum, a transition metal that is widely used in anti-cancer agents, also results in the development of nephropathy due to severe adverse reactions caused by platinum-induced nephrotoxicity. Reports on imaging with metals other than platinum remain are limited, even in preclinical studies. Furthermore, most of these are case reports, and the relationship between the distribution of the metal and clinical observations in human samples is not well understood. Here we report on visualizing lanthanum (139La), a component of Fosrenol, which is usually used for the treatment of hyperphosphatemia. Gastric inflammation, also known as hemorrhagic gastritis, is the main adverse event caused by Fosrenol. To conduct this study, 139La was visualized in gastric biopsy samples obtained from a patient using quantitative laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). We also compared the distribution of 139La in tissue and histochemical results. The areas where 139La accumulated corresponded to the macrophage-positive areas observed in immunohistochemistry studies using an anti-CD68 antibody. In contrast, we observed a debris-like crystal morphology in hematoxylin and eosin staining tissues. The debris was also associated with 139La accumulation. The abnormal accumulation of 139La crystals caused the observed inflammation. This phenomenon was previously characterized, but this is the first report in which 139La distribution and histochemical results are compared using LA-ICP-MS.

The Paleo‐Kuril Arc in the eastern Hokkaido region of Japan, the westernmost part of the Kuril Arc in the northwestern Pacific region, shows a tectonic bent structure. This has been interpreted, using paleomagnetic data, to be the result of block rotations in the Paleo‐Kuril Arc. To understand the timing and origin of this tectonic bent structure in the Paleo‐Kuril arc‐trench system, paleomagnetic surveys and U–Pb radiometric dating were conducted in the Paleogene Urahoro Group, which is distributed in the Shiranuka‐hill region, eastern Hokkaido. The U–Pb radiometric dating indicated that the Urahoro Group was deposited at approximately 39 Ma. Paleomagnetic analysis of the Urahoro Group suggested that the Shiranuka‐hill region experienced a 28° clockwise rotation with respect to East Asia. The degree of clockwise rotation implied from the Urahoro Group is smaller than that of the underlying Lower Eocene Nemuro Group (62°) but larger than that of the overlying Onbetsu Group (−9°). It is thus suggested that the Shiranuka‐hill region experienced a clockwise rotation of approximately 34° between the deposition of the Nemuro and Urahoro Groups (50–39 Ma), and a 38° clockwise rotation between the deposition of the Urahoro and Onbetsu Groups (39–34 Ma). The origin of the curved tectonic belt of the Paleo‐Kuril Arc was previously explained by the opening of the Kuril Basin after 34 Ma. The age constraint for the rotational motion of the Shiranuka‐hill region in this study contradicts this hypothesis. Consequently, it is suggested that the process of arc–arc collision induced the bent structure of the western Paleo‐Kuril Arc.

Despite the recent development in radiometric dating of numerous zircons by LA-ICPMS, mineral separation still remains a major obstacle, particularly in the search for the oldest material on Earth. To improve the efficiency in zircon separation by an order of magnitude, we have designed/developed a new machine – an automatic zircon separator (AZS). This is designed particularly for automatic pick-up of 100 μm-sized zircon grains out of a heavy mineral fraction after conventional separation procedures. The AZS operates in three modes: (1) image processing to choose targeted individual zircon grains out of all heavy minerals spread on a tray, (2) automatic capturing of the individual zircon grains with micro-tweezers, and (3) placing them one-by-one in a coordinated alignment on a receiving tray. The automatic capturing was designed/created for continuous mineral selecting without human presence for many hours. This software also enables the registration of each separated zircon grain for dating, by recording digital photo-image, optical (color) indices, and coordinates on a receiving tray. We developed two new approaches for the dating; i.e. (1) direct dating of zircons selected by LA-ICPMS without conventional resin-mounting/polishing, (2) high speed U-Pb dating, combined with conventional sample preparation procedures using the new equipment with multiple-ion counting detectors (LA-MIC-ICPMS). With the first approach, Pb-Pb ages obtained from the surface of a mineral were crosschecked with the interior of the same grain after resin-mounting/polishing. With the second approach, the amount of time required for dating one zircon grain is ca. 20 s, and a sample throughput of >150 grains per hour can be achieved with sufficient precision (ca. 0.5%).We tested the practical efficiency of the AZS, by analyzing an Archean Jack Hills conglomerate in Western Australia with the known oldest (>4.3 Ga) zircon on Earth. Preliminary results are positive; we were able to obtain more than 194 zircons that are over 4.0 Ga out of ca. 3800 checked grains, and 9 grains were over 4300 Ma with the oldest at 4371 ± 7 Ma. This separation system by AZS, combined with the new approaches, guarantees much higher yield in the hunt for old zircons. Keywords: Hadean, Zircon, U-Pb dating, LA-ICPMS, Automatic mineral separator, Primordial crust

Ecosystem models are used to understand ecosystem dynamics and ocean biogeochemical cycles and require optimum physiological parameters to best represent biological behaviours. These physiological parameters are often tuned up empirically, while ecosystem models have evolved to increase the number of physiological parameters. We developed a three-dimensional (3-D) lower-trophic-level marine ecosystem model known as the Nitrogen, Silicon and Iron regulated Marine Ecosystem Model (NSI-MEM) and employed biological data assimilation using a micro-genetic algorithm to estimate 23 physiological parameters for two phytoplankton functional types in the western North Pacific. The estimation of the parameters was based on a one-dimensional simulation that referenced satellite data for constraining the physiological parameters. The 3-D NSI-MEM optimized by the data assimilation improved the timing of a modelled plankton bloom in the subarctic and subtropical regions compared to the model without data assimilation. Furthermore, the model was able to improve not only surface concentrations of phytoplankton but also their subsurface maximum concentrations. Our results showed that surface data assimilation of physiological parameters from two contrasting observatory stations benefits the representation of vertical plankton distribution in the western North Pacific.

Radiometric calibration utilizing the Moon as a reference source is termed as lunar calibration. It is a useful method for evaluating the performance of optical sensors onboard satellites orbiting the Earth. Lunar calibration provides sufficient radiometric calibration opportunities without requiring any special equipment, and is suitable for nano/microsatellites. This study applies lunar calibration to a multispectral sensor, Ocean Observation Camera (OOC), on board a microsatellite named Rapid International Scientific Experiment Satellite. Simulating the brightness of the Moon based on the RObotic Lunar Observatory and SELENE/Spectrum Profiler models, sensitivity degradation was proven to be negligible in any of the four spectral bands of the OOC with the sensor temperature correction. A bluing trend in the OOC’s sensor sensitivity was revealed, indicating a shorter observation wavelength shows larger irradiance. Comparing the top-of-atmosphere reflectance of Railroad Valley Playa with the Radiometric Calibration Network dataset revealed that the derived calibration parameter from the lunar calibration was valid for correcting the bluing trend in the visible range. Although the lunar and vicarious calibration parameters for the infrared band were unexpectedly inconsistent, lunar calibration could potentially contribute toward estimating the contaminated background radiance in the Earth observation images.

In the eastern North China Craton, basement gneisses are covered by poorly dated Late Paleoproterozoic to Early Neoproterozoic sediments. This study reports new zircon data from the Jixian area to constrain the protolith age of basement orthogneisses, the detrital ages of cover clastic sediments, and the age of a post-tectonic intrusive granite. Most zircons in orthogneisses have dark cores and bright rims in cathodoluminescence images. The dark cores have 207Pb/206Pb peak ages at 2520 Ma that constrain the minimum protolith age of the orthogneiss. In contrast, the bright rims have a wide 207Pb/206Pb age range from ca. 2500 Ma to 1800 Ma that is distributed along the Concordia curve, which reflect a Paleoproterozoic overprint on the basement of the North China Craton. Overlying clastic sediments mainly contain 2.5–2.7 Ga zircons derived from the basement rocks. 2200 Ma detrital oscillatory-zoned zircons, especially in a basal conglomerate of the Xiamaling Fm., were no doubt derived from 2200 Ma igneous rocks, probably from the southern North China Craton. The intrusive granite contains euhedral zircon grains with clear oscillatory zones that yield a Concordia age of 205.6 ± 1.1 Ma, and was likely generated during early Mesozoic delamination of the eastern North China Craton.

Understanding Earth’s early evolution requires decoding the cryptic geological record that is preserved in a few extremely rare terrains on Earth. The Saglek–Hebron Block in the North Atlantic Craton is one of the oldest terrains in the world. To better understand the Eoarchean history of the Saglek–Hebron Block, we undertook a comprehensive geological and geochronological investigation of this terrain. The Saglek–Hebron locality contains orthogneisses and supracrustal rocks, which are classified into two groups of the Eoarchean and Mesoarchean suites based on field associations defined by intrusion of the Mesoarchean mafic Saglek dykes. The Eoarchean suites contain the Nulliak supracrustal rocks and Uivak Gneisses. In this paper, we report cathodoluminescence (CL) observations and U–Pb ages of zircons from the Eoarchean orthogneisses to constrain the evolution of the Saglek–Hebron Block. We made detailed sketch maps (1:20) of critical outcrops to establish relative chronological relationships between lithologies. At least seven generations of mafic and felsic units were recognized in an outcrop of the St John’s Harbour South area. The first and second generations are mafic supracrustal rocks whereas the third to seventh generations are tonalitic gneisses, which are intruded into the supracrustal units. We study CL observation, geochemistry and U–Pb dating of zircons from the oldest and youngest tonalitic gneisses. The CL observation of internal structures of the zircons showed they typically comprise three domains of core, mantle and rim. The cores have clear oscillatory zoning, whereas the mantles lack oscillatory zoning and exhibit dark CL emission and structureless CL images. The obvious correlation between the ages and chemical compositions of U contents and Th/U ratios indicates that the cores with low U contents and high Th/U ratios preserve the protolith age. The cores with clear oscillatory zoning, low U contents and high Th/U ratios of zircons from the oldest suite plot on a concordia line with ages ranging from 3953 to 3797 Ma. The oldest and average ages of the six oldest spots on the concordia line are 3953 ± 54 and 3920 ± 49 Ma, respectively. On the other hand, the average age of the four old spots of zircons from a younger generation of orthogneiss is 3869 ± 63 Ma. The geological and geochronological relationships between the third and seventh generation orthogneisses are consistent with each other, confirming an Eoarchean age of ca. 3.9 Ga for the oldest suite of the Uivak Gneisses. We name this oldest suite the Iqaluk Gneiss. As the protolith of the Iqaluk Gneiss was clearly intruded into the Nulliak supracrustal rocks, the Nulliak supracrustals must have a minimum age of ca. 3.9 Ga, indicating that they are the oldest supracrustal rocks on Earth. But, further studies should be necessary to obtain more precise age of the Iqaluk Gneiss and Nulliak supracrustal rocks.

The Ninth Symposium on Polar Science/Ordinary sessions: [OG] Polar Geosciences, Wed. 5 Dec. / 3F Seminar room, National Institute of Polar Research

We compared the functional response of a biogeochemical data assimilation model versus an empirical satellite-derived algorithm in describing the variation of four phytoplankton (diatoms, cyanobacteria, coccolithophores and chlorophytes) groups globally and in 12 major oceanographic basins. Global mean differences of all groups were within ~ 15% of an independent observation data base for both approaches except for satellite-derived chlorophytes. Diatoms and cyanobacteria concentrations were significantly (p < 0.05) correlated with the independent observation data base for both methods. Coccolithophore concentrations were only correlated with the in situ data for the model approach and the chlorophyte concentration was only significantly correlated to the in situ data for the satellite-derived approach. Using monthly means from 1998–2007, the seasonal variation from the satellite-derived approach and model were significantly correlated in 11 regions for diatoms and in 9 for coccolithophores but only in 3 and 2 regions for cyanobacteria and chlorophytes. Most disagreement on the seasonal variation of phytoplankton composition occurred in the North Pacific and Antarctic where, except for diatoms, no significant correlation could be found between the monthly mean concentrations derived from both approaches. In these two regions there was also an overestimate of diatom concentration by the model of ~ 60% whereas the satellite-derived approach was closer to in situ data (8–26% underestimate). Chlorophytes were the group for which both approaches differed most and that was furthest from the in situ data. These results highlight the strengths and weaknesses of both approaches and allow us to make some suggestions to improve our approaches to understanding phytoplankton dynamics and distribution.

To evaluate the group-specific primary production of diatoms, haptophytes, and cyanobacteria in the Kuroshio region, a novel satellite observation methodology using the SeaStar/SeaWiFS satellite instrument was developed. The method used bio-optical relationships between the group-specific production and bio-optical properties such as the photosynthetic quantum yield and chlorophyll a specific optical absorption coefficient of phytoplankton, the last two of which were also estimated together with the group-specific production rather than assumed a priori. A global property of the absorption coefficient of phytoplankton, that the coefficient value at the wavelength of 510 nm was close to their spectral average, was highlighted in the method for a use of multi-spectral ocean color satellite data. Our results showed that the derived quantum yield index was higher for diatoms than haptophytes and cyanobacteria. Furthermore, intraspecific variation in the index, emerged as a latitudinal gradient: the values for cyanobacteria increased towards the higher latitudes. The group-specific primary production in the Kuroshio region showed that the climatological average of 134, 72 and 40 mg C m−2 day−1 for diatoms, haptophytes, and cyanobacteria, respectively. A comparison among variability of the group-specific primary production, the quantum yield index, and the absorption coefficient suggested that, in the Kuroshio region, the primary production due to diatoms was driven by their abundance through the year, whereas that due to cyanobacteria by photophysiology. The production due to haptophytes was seasonally regulated by both abundance and photophysiology.

Here, we report a new ‘discovery’ of a desmostylian fossil in the geological collection at a national university in Japan. This fossil was unearthed over 60 years ago and donated to the university. Owing to the original hand-written note kept with the fossil in combination with interview investigation, we were able to reach two equally possible fossil sites in the town of Tsuchiyu Onsen, Fukushima. Through the interviews, we learned that the fossil was discovered during construction of a debris flow barrier and that it was recognized as a ‘dinosaur’ bone among the locals and displayed in the Village Hall before/until the town experienced a fire disaster in 1954. As scientific findings, the fossil was identified to be a right femur ofPaleoparadoxia(Desmostylia), which shows well-preserved muscle scars on the surface. The age was estimated to be 15.9 Ma or younger in zircon-dating. This study shows an excellent case that historical and scientific significances could be extracted from long-forgotten uncatalogued specimens as long as the original information is retained with the specimens.

The Gwna Group in Anglesey island and Lleyn peninsula, Wales consists of a latest Proterozoic volcano-sedimentary trench melange, which has a complicated accretionary structure, and is poorly constrained by isotopic ages. The melange contains oceanic-trench rocks including pillow basalts, cherts, mudstones and sandstones, which have not previously been interpreted as ocean plate stratigraphy (OPS). We reconstructed imbricated OPS at 5 localities in the coastal Lleyn peninsula. In order to constrain the depositional U–Pb age of the upper clastic sediments, detrital zircons, separated from 9 clastic sediments, were analyzed with a Nu AttoM single-collector inductively-coupled plasma-mass spectrometer. The ages indicate that there are two Gwna Groups (maximum depositional ages of: 1 at 608–601 Ma, and 2 at 564–539 Ma) that were deposited between the late Neoproterozoic and the Middle Cambrian contemporaneously with dated calc-alkaline arc magmatism and regional metamorphism in the Anglesey–Lleyn complex. The age spectra of the detrital zircons show a prominent peak at ca. 650–600 Ma, and several Proterozoic and Archean ages. To account for the older ages, we integrated our new isotopic data with published radiometric and fossil ages, and conclude that the clastic sediments at the top of the OPS were deposited in a trench on the western active margin of Avalonia when it was close to the Amazonian craton, and that the Gwna Group OPS began to be incorporated into an accretionary wedge in an active subduction zone in the latest Proterozoic.

The Ballantrae Complex (at Bennane Lea in SW Scotland) contains important ocean plate stratigraphy (basalt, chert, mudstone, sandstone) in an accretionary prism that is associated with a classic Ordovician ophiolite. We used the ocean plate stratigraphy to sub-divide the prism into 11 tectonic units. To determine the depositional age of bedded cherts, zircons were separated from 9 tuff beds from 6 different units. All the tuffs have early to middle Ordovician ages, even though their present positions are mutually distant. These ages are consistent with microfossil records of radiolaria and graptolites. The stratigraphic–structural relationships demonstrate that the ocean plate stratigraphy has been repeated by bedding-parallel thrusts; this is typical of a modern accretionary duplex. We calculated the sedimentation rate of Early to Middle Ordovician bedded cherts at Bennane Lea on the basis of U–Pb zircon ages obtained from several tuff beds; the data indicate that the depositional rate (0.6–3 m/myr) was as slow as that of Mesozoic–Cenozoic equivalents defined by radiolaria. The age spectra of detrital zircons from Ballantrae sandstones show prominent single peaks at ca. 467 and 478 Ma, and a lack of Precambrian zircons. Integration of our new zircon ages with published isotopic data and palaeo-geographic maps indicates that the sandstones were deposited near an intra-oceanic arc and far from any continent containing Precambrian rocks. The pelagic-to-clastic sediments at Bennane Lea were deposited in the closing Iapetus Ocean from ca. 477 Ma to ca. 464 Ma, when they were accreted with the intra-oceanic arc of Ballantrae.

Knowledge of the lithological variability and genesis of island arc crust is important for understanding continental growth. Although the volcanic architecture of island arcs is comparatively well known, the nature of island arc middle- and lower-crust remains uncertain owing to limited exposure. One of the best targets for deciphering the evolution of an island arc system is the Tanzawa Tonalites (4–9 Ma), in the intra-oceanic Izu–Bonin–Mariana arc. These tonalities which occupied a mid-crustal position were generated by partial melting of lower crust. To constrain protoliths of the plutonic rocks in the island arc lower crust, in-situ O-isotopic analysis using an IMS-1280 Secondary Ion Mass Spectrometer was carried out on 202 zircon grains separated from 4 plutons in the Tanzawa Tonalite. δ18O value of the zircons ranges from 4.1‰ to 5.5‰ and some zircons have δ18O slightly lower than the mantle range. The low zircon δ18O values from the Tanzawa Tonalite suggest that their protoliths involved materials with lower δ18O values than those of the mantle. Hydrothermally altered gabbros in the lower oceanic crust often have lower δ18O values than mantle and can be primary components of arc lower crust. The Tanzawa Tonalite is interpreted to have been formed by partial melting of island arc lower crust. Thus the low δ18O values in zircons from the Tanzawa Tonalites may originate by melting of the hydrothermally altered gabbro. Ancient oceanic crustal material was likely present in the Izu–Bonin–Mariana arc lower crust, at the time of formation of the Tanzawa Tonalites.

The timing of the emergence of life remains one of the principal unresolved questions in the Earth sciences. Putative relicts of microorganisms in the Eoarchean ( ca. 3.6–3.85 Ga) high-grade metamorphic terranes do not preserve morphological evidence for early life, but some relicts can be identified by their geochemical signatures created by metabolic processes. Among the oldest rocks of sedimentary origin ( ca . 3.8 Ga) occur in the Isua supracrustal belt (ISB), southern West Greenland; these have undergone metamorphism up to the amphibolite facies. Despite intense metamorphism, the carbon isotope compositions of graphite clots from the Isua metasedimentary rocks suggest biological carbon fixation and provide the oldest evidence for this biological process. Microbial dissimilatory iron reduction (DIR) is considered to be an early form of metabolism. The microbial DIR produced Fe 2 + aq with a lower δ 56 Fe value from a precursor Fe 3 + -bearing iron mineral. However, δ 56 Fe values lower than − 1‰ are not found in sedimentary rocks prior to about 2.9 Ga. Here, we report in-situ iron isotope analysis of pyrites in sedimentary rocks from the ISB, using a near infrared-femtosecond-laser ablation-multicollector-ICP-MS (NIR-fs-LA-MC-ICP-MS). A large variation of δ 56 Fe values from − 2.41 to + 2.35‰, was documented from 190 points within pyrite grains from 11 rock specimens, including those interpreted to be banded iron-formations (BIFs), chert, amphibole-rich chert, quartz-rich clastic sedimentary rocks, mafic clastic sedimentary rocks, carbonate rocks and conglomerates. We found that the distribution of δ 56 Fe values depends on the lithology, whereas there is no correlation between their δ 56 Fe values and the metamorphic grade. The δ 56 Fe values of pyrites in BIFs range from + 0.25 to + 2.35‰, indicating partial oxidation in the deep ocean. Especially, the high δ 56 Fe values, up to + 2.35‰, suggest that the BIF was formed through interaction of ferruginous seawater with a highly alkaline hydrothermal fluid under anoxic conditions. Pyrite grains in a conglomerate, carbonate rocks, mafic clastic sedimentary rocks, and amphibole-rich cherts show negative δ 56 Fe values around − 1.5‰, down to − 2.41‰, pointing to microbial DIR in the Eoarchean shallow sea. In addition, the relatively low δ 56 Fe values of pyrites in the shallow water sediments suggest anoxic, anoxygenic photoautotrophic iron oxidation in the photic zone.

The Neoproterozoic Era records several important events in Earth history. The associations between BIF deposition, Snowball Earth events and the redox state of seawater are the key to explain the re-appearance of banded iron formations (BIF) during the Neoproterozoic. Unraveling ancient iron cycles provides important information about the linkage between the precipitation of BIF and the redox condition in the ocean, but current iron isotopic data are limited to sediments deposited only during the Sturtian glaciations and Ediacaran. We conducted a detailed geological survey of the Tonian to Ediacaran sedimentary succession in Nordaustlandet island, Svalbard. Our chemostratigraphies of δ 13 C carb from pre-Sturtian to post-Marinoan sedimentary successions in the Polarisbreen Group are consistent with those in coeval sediments. We first analyzed iron isotope ratios (δ 56/54 Fe) of individual pyrite grains with diverse shapes in carbonates, black shales, quartz arenites and diamictites in order to constrain the redox condition in seawater. We found large variations in iron isotope ratios; from ca. −2 to ca. +4‰. Positive δ 56/54 Fe values, over +1.0‰, are only preserved in euhedral and aggregated pyrite grains in black shales of the Backlundtoppen Formation and the MacDonaldryggen Member of the Elbobreen Formation. A partial oxidation of ferrous iron in seawater is necessary to explain such high δ 56/54 Fe values, which means that deep seawater was ferruginous (ferrous, iron-rich) before and after the Sturtian glaciation. This stands in opposition to the traditional idea that a glacial cover on an ocean is necessary for the accumulation of ferrous iron in Neoproterozoic seawater. This study presents the first evidence from iron isotopes that supports a deep ferruginous ocean around the Sturtian glaciation. If the deep ocean was intrinsically iron-rich, it is likely that Neoproterozoic BIFs formed by thermohaline circulation during the glaciation and by massive oxidation due to the expansion of oxic oceans after the glaciation.