This paper contains a series of essays which form a synopsis of my research career, which has been dedicated to orogenic and metamorphic processes in plate boundaries. It also presents my future research directions and latest investigations into simplifying the complexity of metamorphic rocks, their field observations, and associated convergent plate margin dynamics.
Slab dehydration beneath forearcs and arc has been one of the most exciting problems in the field of convergent plate margin dynamics in recent decades. Orogenic and metamorphic processes are closely related. In the subduction zones, the fluid-mediated processes primarily control the crust-to-mantle transfer of volatiles, redox states of the wedge mantle peridotite and arc magmas, flux-melting to generate arc magmas, and seismicity. Although the methods of classical metamorphic petrology, based on phase equilibrium calculations, and the application of conventional geochronology continue to provide the opportunities to link high-pressure and ultra-high-pressure metamorphism to geophysical observations today, advances in geochemical techniques have great potential for key geological markers in global convergent margins. For example, recent analytical techniques and applications used in studies of metamorphic rocks, such as in-situ Li-B-Sr-Pb spot isotope analyses of jadeite, serpentinite, lawsonite, etc., evaluate hydration and dehydration along the subduction channels and subsequent slab-mantle interaction, and visualize more realistic ancient Pacific-type convergent margins. The scientific value of subduction-zone rocks and crustal rocks are not limited to their worth for geochemistry: Some metamorphic rocks and minerals are important for all realms of geological sciences, from nano-scale kinetics to the scale of mountain building events. Consequently, collaborative exchange among geoscientists, through the application of applying different approaches, tests, and challenges, to address problems related to plate boundaries in the future.
Astromineralogy has developed as an interdisciplinary field between astronomy and mineralogy since the discovery of crystalline silicate dust from stellar atmospheres by infrared observations in the late 1990s. Cosmic dust repeatedly forms and is destroyed along with the physical evolution of stars, and thus is a carrier of metallic elements in the galactic material circulation. Minerals found in the solar system and on Earth are observed outside the solar system as well. In addition, presolar grains are the very survivors of circumstellar dust, and are the key to understanding the observed dust and its formation process. Understanding the galactic material circulation through the formation and evolution of cosmic dust requires knowledge not only of astronomy but also of petrology and mineralogy. In this paper, I review the progress of astromineralogy including the author's research and discuss how mineralogy has contributed to the development of astromineralogy.
For the past 30 years, I have performed a mineralogical study of various kinds of extraterrestrial materials focusing on evolution processes of Solar System bodies. The samples analyzed range from primitive chondritic materials returned by spacecrafts to differentiated meteorites including Martian and lunar samples. The first of these analyzed meteorites was an angrite, one of the oldest known achondrites, in collaboration with researchers at NASA's Johnson Space Center, USA. I pointed out the importance of olivine xenocrysts by studying many quenched angrites and showed that bulk compositions of quenched angrites were controlled by resorption degrees of these xenocrysts. Soon I became involved in studying Martian meteorites. In my early works, I found that some shergottite Martian meteorites experienced undercooling of magma and represented parent magma compositions by combining crystallization experimental results. I also revealed that nakhlite Martian meteorites had correlated petrography and mineralogy that could be explained by crystallization at different locations (burial depths) in a common cooling cumulate pile. The presence of remarkable shock features (e.g., darkening of olivine) in Martian meteorites is striking, and it appears that prolonged post-shock heating history largely erased the high-pressure polymorphs in many cases. My research deals with primitive solar system materials including Wild 2 cometary particles and Itokawa asteroidal particles. Studying these samples using electron beam and synchrotron radiation analyses has strengthened the interpretations of their origins. Another important tool employed is electron backscatter diffraction (EBSD) analysis. I applied this technique to identify several new minerals such as dmitryivanovite, andreyivanovite, and kushiroite in early 2000s. EBSD was also used to analyze preferred crystallographic orientation of olivine in brachinites, revealing rigorous magmatic and/or rheological activities in the parent body. At present I am analyzing Ryugu samples returned by the Hayabusa2 spacecraft as a preliminary analysis team member, which broadens our understanding of the formation and evolution processes of solid materials in the early Solar System.
Information collected from geological newsmagazines in 2021 is reviewed. First topic is mineral resources such as mineral commodity summary in USA, resource potential of the East Siberia, and mineralogy of Ettringite and Nepheline. Second topic is the historical building stones, that is, review of IGCP-637, a bluish granite in Spain, and the Firenze building stone. Third is alternative interpretation of the Anthropocene, considering one of the geological epochs or not.
We can find various nano-scale materials and an abundance of recipes in nature, which offer many potential benefits in our life and contribute to create a sustainable society. Natural Clay minerals are known as safe substances with moderate stability even under the influence of various external environments such as temperature, pressure, and pH value. In addition, they have notable properties. They are ion-exchangeable, excellent adsorbents, and swellable, and thus have been used in various forms in society. This article introduces the development of environmentally friendly clay polymer nanocomposites and high-performance caffeine-adsorbing materials that skillfully utilize clay minerals.
Mantle deformation is closely related to plate motion, earthquakes, and volcanic activities. In previous experimental studies, the rheological properties of the mantle rocks have been determined based on assumptions that the mantle rocks are composed of single-phase crystal aggregates with a homogeneous chemical composition, and the mechanical data and rock microstructure reach a steady-state even at small strain. However, it is obvious that these assumptions oversimplify the complexity of natural rocks. To overcome such limitations, the author conducted various types of deformation experiments to investigate the rheological properties of rocks by taking into account the secondary mineral phases, different iron content of olivine, and different strain. The obtained results allow us to understand the mantle flow under more realistic conditions. In this paper, I would like to introduce the recent results of high-strain torsion experiments using a Patterson-type gas-medium apparatus.