CO2-rich komatiitic melt inclusions in Cr-spinels within beach sand from Gorgona Island, Colombia

Author Posting. © The Author(s), 2009. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Earth and Planetary Science Letters 288 (2009): 33-43, doi:10.1016/j.epsl.2009.09.005.The volatile content of komatiite is a key to constrain the thermal and chemical evolution of the deep Earth. We report the volatile contents with major and trace element compositions of ~ 80 melt inclusions in chromian spinels (Cr-spinels) from beach sands on Gorgona Island, Colombia. Gorgona Island is a ~ 90 Ma volcanic island, where picrites and the youngest komatiites known on the Earth are present. Melt inclusions are classified into three types on the basis of their host Cr-spinel compositions: low Ti (P type), high Ti with high Cr# (K1 type) and high Ti with low Cr# (K2 type). Chemical variations of melt inclusions in the Cr-spinels cover all of the island's lava types. P-type inclusions mainly occur in the picrites, K1-type in high-TiO2 komatiites (some enriched basalts: E-basalts) and K2-type in low-TiO2 komatiites. The H2O and CO2 contents of melt inclusions within Cr-spinels from the beach sand are highly variable (H2O: 0.03–0.9 wt.%; CO2: 40–4000 ppm). Evaluation of volatile content is not entirely successful because of compositional alterations of the original melt by degassing, seawater/brine assimilation and post-entrapment modification of certain elements and volatiles. However, the occurrence of many melt inclusions with low H2O/K2O ratios indicates that H2O/K2O of Gorgona komatiite is not much different from that of modern mid-oceanic ridge basalt (MORB) or oceanic island basalt. Trend of CO2/Nb and Zr/Y ratios, accounted for by two-component mixing between the least degassed primary komatiite and low-CO2/Nb evolved basalt, allow us to estimate a primary CO2/Nb ratio of 4000 ± 2200 or a CO2 content of 0.16 ± 0.09 wt.%. The determined CO2/Nb ratio is unusually high, compared to that of MORB (530). Although the presence of CO2 in the Gorgona komatiite does not affect the magma generation temperature, CO2 degassing may have contributed to the eruption of high-density magmas. High CO2/Nb and the relatively anhydrous nature of Gorgona komatiite provide possible resolution to one aspect of the hydrous komatiite debate.This work is financially supported by grants from the Japan Society for the Promotion of Science

Petrology and Geochemistry of Boninite Series Volcanic Rocks,Chichi-jima, Bonin Islands, Japan

An Eocene submarine boninite series volcanic center isexposed on the island of Chichi-jima, Bonin Islands, Japan. Five rocktypes, boninite, bronzite andesite, dacite, quartz dacite, and rhyolite,were distinguished within the boninite volcanic sequence on the basis ofpetrographic and geochemical observations. Boninite lavas contain highmagnesium, nickel, and chromium contentsindicative of primitive melts,but have high silica contents relative to other mantle-derived magmas.All boninite series lavas contain very low incompatible elementconcentrations, and concentrations of high-field strength elements inprimitive boninite lavas are less than half of those found in depletedmid-ocean ridge basalts. Abundances of large-ion lithophile elements arerelatively high in boninite series lavas, similar to the enrichmentsobserved in many island arc lavas. Trends for both major and traceelement data suggest that the more evolved lavas of the boninite magmaseries were derived primarily through high-level fractionalcrystallization of boninite. Textural features, such as resorption andglomeroporphyrocrysts, and reverse chemical zonations suggest that magmamixing contributed to the development of the quartz dacitelavas

The Relationship Between Microbial Community Structures and Environmental Parameters Revealed by Metagenomic Analysis of Hot Spring Water in the Kirishima Area, Japan

Diverse microorganisms specifically inhabit extreme environments, such as hot springs and deep-sea hydrothermal vents. To test the hypothesis that the microbial community structure is predictable based on environmental factors characteristic of such extreme environments, we conducted correlation analyses of microbial taxa/functions and environmental factors using metagenomic and 61 types of physicochemical data of water samples from nine hot springs in the Kirishima area (Kyusyu, Japan), where hot springs with diverse chemical properties are distributed in a relatively narrow area. Our metagenomic analysis revealed that the samples can be classified into two major types dominated by either phylum Crenarchaeota or phylum Aquificae. The correlation analysis showed that Crenarchaeota dominated in nutrient-rich environments with high concentrations of ions and total carbons, whereas Aquificae dominated in nutrient-poor environments with low ion concentrations. These environmental factors were also important explanatory variables in the generalized linear models constructed to predict the abundances of Crenarchaeota or Aquificae. Functional enrichment analysis of genes also revealed that the separation of the two major types is primarily attributable to genes involved in autotrophic carbon fixation, sulfate metabolism and nitrate reduction. Our results suggested that Aquificae and Crenarchaeota play a vital role in the Kirishima hot spring water ecosystem through their metabolic pathways adapted to each environment. Our findings provide a basis to predict microbial community structures in hot springs from environmental parameters, and also provide clues for the exploration of biological resources in extreme environments

The Argyre Region as a Prime Target for in situ Astrobiological Exploration of Mars

At the time before ∼3.5 Ga that life originated and began to spread on Earth, Mars was a wetter and more geologically dynamic planet than it is today. The Argyre basin, in the southern cratered highlands of Mars, formed from a giant impact at ∼3.93 Ga, which generated an enormous basin approximately 1800 km in diameter. The early post-impact environment of the Argyre basin possibly contained many of the ingredients that are thought to be necessary for life: abundant and long-lived liquid water, biogenic elements, and energy sources, all of which would have supported a regional environment favorable for the origin and the persistence of life. We discuss the astrobiological significance of some landscape features and terrain types in the Argyre region that are promising and accessible sites for astrobiological exploration. These include (i) deposits related to the hydrothermal activity associated with the Argyre impact event, subsequent impacts, and those associated with the migration of heated water along Argyre-induced basement structures; (ii) constructs along the floor of the basin that could mark venting of volatiles, possibly related to the development of mud volcanoes; (iii) features interpreted as ice-cored mounds (open-system pingos), whose origin and development could be the result of deeply seated groundwater upwelling to the surface; (iv) sedimentary deposits related to the formation of glaciers along the basin's margins, such as evidenced by the ridges interpreted to be eskers on the basin floor; (v) sedimentary deposits related to the formation of lakes in both the primary Argyre basin and other smaller impact-derived basins along the margin, including those in the highly degraded rim materials; and (vi) crater-wall gullies, whose morphology points to a structural origin and discharge of (wet) flows

Assessment of epigenetic alterations in early colorectal lesions containing BRAF mutations

金沢大学医薬保健学総合研究科先進的地域医療研究講座 = Department of Advanced Research in Community MedicineTo clarify the molecular and clinicopathological characteristics of colorectal serrated lesions, we assessed the DNA methylation of cancer-associated genes in a cohort of BRAF-mutant precancerous lesions from 94 individuals. We then compared those results with the lesions’ clinicopathological features, especially colorectal subsites. The lesions included hyperplastic polyps (n = 16), traditional serrated adenomas (TSAs) (n = 15), TSAs with sessile serrated adenomas (SSAs) (n = 6), SSAs (n = 49) and SSAs with dysplasia (n = 16). The prevalence of lesions exhibiting the CpG island methylator phenotype (CIMP) was lower in the sigmoid colon and rectum than in other bowel subsites, including the cecum, ascending, transverse and descending colon. In addition, several cancer-associated genes showed higher methylation levels within lesions in the proximal to sigmoid colon than in the sigmoid colon and rectum. These results indicate that the methylation status of lesions with BRAF mutation is strongly associated with their location, histological findings and neoplastic pathways. By contrast, no difference in aberrant DNA methylation was observed in normal-appearing background colonic mucosa along the bowel subsites, which may indicate the absence of an epigenetic field defect

Origin of the Earth: A proposal of new model called ABEL

The Earth was born as a dry planet without atmosphere and ocean components at 4.56 Ga, with subsequent secondary accretion of bio-elements, such as carbon (C), hydrogen (H), oxygen (O), and nitrogen (N) which peaked at 4.37–4.20 Ga. This two-step formation model of the Earth we refer to as the advent of bio-elements model (ABEL Model) and the event of the advent of bio-elements (water component) as ABEL Bombardment. It is clear that the solid Earth originated from enstatite chondrite-like dry material based on the similarity in oxygen isotopic composition and among other isotopes. On the other hand, Earth's water derives primarily from carbonaceous chondrite material based on the hydrogen isotopic ratio. We present our ABEL model to explain this enigma between solid Earth and water, as well as secondary accretion of oxidizing bio-elements, which became a precursor to initiate metabolism to emerge life on a highly reductive planet. If ABEL Bombardment had not occurred, life never would have emerged on the Earth. Therefore, ABEL Bombardment is one of the most important events for this planet to evolve into a habitable planet. The chronology of ABEL Bombardment is informed through previous researches of the late heavy bombardment and the late veneer model. ABEL Bombardment is considered to have occurred during 4.37–4.20 Ga, which is the concept to redefine the standard late heavy bombardment and the late veneer models. Also, ABEL Bombardment is the trigger of the transition from stagnant lid tectonics to plate tectonics on this planet because of the injection of volatiles into the initial dry Earth

Origins of building blocks of life: A review

How and where did life on Earth originate? To date, various environments have been proposed as plausible sites for the origin of life. However, discussions have focused on a limited stage of chemical evolution, or emergence of a specific chemical function of proto-biological systems. It remains unclear what geochemical situations could drive all the stages of chemical evolution, ranging from condensation of simple inorganic compounds to the emergence of self-sustaining systems that were evolvable into modern biological ones. In this review, we summarize reported experimental and theoretical findings for prebiotic chemistry relevant to this topic, including availability of biologically essential elements (N and P) on the Hadean Earth, abiotic synthesis of life's building blocks (amino acids, peptides, ribose, nucleobases, fatty acids, nucleotides, and oligonucleotides), their polymerizations to bio-macromolecules (peptides and oligonucleotides), and emergence of biological functions of replication and compartmentalization. It is indicated from the overviews that completion of the chemical evolution requires at least eight reaction conditions of (1) reductive gas phase, (2) alkaline pH, (3) freezing temperature, (4) fresh water, (5) dry/dry-wet cycle, (6) coupling with high energy reactions, (7) heating-cooling cycle in water, and (8) extraterrestrial input of life's building blocks and reactive nutrients. The necessity of these mutually exclusive conditions clearly indicates that life's origin did not occur at a single setting; rather, it required highly diverse and dynamic environments that were connected with each other to allow intra-transportation of reaction products and reactants through fluid circulation. Future experimental research that mimics the conditions of the proposed model are expected to provide further constraints on the processes and mechanisms for the origin of life. Keywords: Astrobiology, Biochemistry, Chemical evolution, Extraterrestrial life, Hadean Earth, Hydrothermal system

Inclusion study in zircon from ultrahigh-pressure metamorphic rocks in the Kokchetav massif : an excellent tracer of metamorphic history

Zircon is an excellent material to preserve the complex history of ultrahigh-pressure (UHP) metamorphic rocks, whereas mineralogical evidence of UHP conditions is mostly obliterated in matrix assemblages as a result of extensive retrograde overprinting during exhumation. Zircons from the Kokchetav UHP-HP massif contain numerous inclusions of graphite, quartz, garnet, omphacite, jadeite, phengite, phlogopite, rutile, albite, K-feldspar, amphibole, zoisite, kyanite, calcite, dolomite, apatite and monazite, as well as the diagnostic UHP minerals, such as microdiamond and coesite, which were identified by laser Raman spectroscopy. The internal structure of zircon displays a distinct zonation, which comprises an inherited core, a wide mantle and an outer rim, each with distinctive inclusion micro-assemblages. The low-pressure mineral inclusions, such as graphite, quartz and albite, are common in the inherited core and thin outer rim, whereas diamond, coesite and jadeite occupy the mantle domain. The zircon core and Outer rim are of detrital and relatively low-grade metamorphic origin, whereas the mantle domain is of HP to UHP metamorphic origin. The mineral assemblages and chemistry of inclusions preserved in zircon have been used to constrain the metamorphic P-T path of the Kokchetav UHP-HP rocks, and indicate peak metamorphism at 60-80 kbar and 970-1100 degrees C followed by nearly isothermal decompression at 10 kbar and c. 800 degrees C. Sensitive high-resolution ion microprobe U-Pb spot analyses of the zoned zircon indicate four discrete ages of the Kokchetav metamorphic evolution: (1) a Middle Proterozoic protolith age; (2) 537 +/- 9 Ma for UHP metamorphism; (3) 507 +/- 8 Ma for the late-stage amphibolite-facies overprint; (4) 456-461 Ma for post-orogenic thermal events. This indicates that Middle Proterozoic supracrustal protoliths of the Kokchetav UHP-HP rocks were subducted to mantle depths in the Middle Cambrian, and exhumed to mid-crustal levels in the Late Cambrian. The zonal arrangement of inclusions and the presence of coesite and diamond without back reaction imply that aqueous fluids were low to absent within zircon, and that zircon is capable of retaining minerals of each metamorphic stage. We Suggest that the study of inclusions in zircon is a powerful method to clarify the multiple stages and timing of metamorphic evolution of UHP-HP rocks, the evidence for which has been more or less obliterated in the host rock