The timing and duration of fault-zone activity remain inadequately constrained, impeding quantitative insight into brittle deformation processes and earthquake-cycle dynamics. Authigenic minerals precipitated within fault zones constitute direct archives of deformation and hydrothermal fluid flow, enabling fault activity to be dated independently of displaced stratigraphic markers. Recent advances in fault geochronology—most notably illite K–Ar/Ar–Ar, hematite (U–Th)/He, and calcite U–Pb—have established robust temporal constraints on deformation and fluid-related events. By contrast, the geochronological potential of silica minerals, particularly quartz and opal, remains insufficiently developed despite their pronounced sensitivity to brittle failure, seismic cycling, and hydrothermal processes. Silica undergoes repeated dissolution–precipitation in hydrothermal systems and can selectively incorporate uranium; however, fundamental constraints on uranium uptake, retention, and system behavior are sparse. While recent in-situ studies demonstrate the feasibility of dating fault-related silica, significant methodological challenges persist. Concurrently, evidence that fault-hosted opal records earthquake-related fluid discharge, and that quartz vein formation is closely coupled to fault-valve behavior, underscores the need for a systematic framework. Here we develop an integrated approach to uranium-series geochronology of quartz and opal, building on the achievements and limitations of calcite-based methods. Focusing on the Japan arc system, where silica veins are widespread and geological, seismic, and geodetic constraints are extensive, we combine microstructural, geochemical, and isotopic analyses to resolve high-resolution temporal records of brittle deformation and fluid migration from shallow to mid-temperature crustal regimes.

Polarizing microscopy remains fundamental to petrography, even as electron-beam microanalysis and electron backscatter diffraction have replaced many quantitative determinations. This paper re-evaluates the method’s capabilities and limits from the perspective of the Maxwell equation, which reveals that almost all optical features observed in polarizing microscopy are consequences of a mineral’s dielectric permittivity tensor. This viewpoint makes the method’s constraints explicit: compositional estimation and orientation determination are inherently restricted, particularly relative to SEM-based approaches including EBSD. Nevertheless, polarizing microscopy retains a practical advantage in throughput, providing an effective route for rapid, thin-section–scale analysis of rock microtextures. The paper introduces the author’s recent work on NicoNavi, a tool developed to streamline data extraction from polarizing-microscope observations within a unified workflow and discusses how such approaches can reposition polarizing microscopy as an entry point to data-driven petrography.

Advances in ion-beam technology with high spatial resolution and detectors with high sensitivity have enabled the development of high-precision and high-resolution mass spectrometry analyses for rock samples. However, the combination of isotope analysis at levels of a few to tens of ppm and high-resolution at scales of tens of μm remains underexplored. This is primarily due to delays in developing site-specific sampling methods for preparing rock samples into solutions. In this manuscript, I propose new sampling methods aimed at future advancements in cosmochemistry and geochemistry. Focused ion beam and laser ablation technologies are promising for flexible and precise sample cutting and should be adopted as new sampling methods in cosmochemistry and geochemistry. In particular, the flexibility of laser ablation operation allows for three-dimensional (3D) cutting and analysis of samples, expanding upon traditional two-dimensional (2D) analysis. Three-dimensional analyses facilitate observation and sampling of thin layers as curved surfaces, which are challenging to analyze using 2D methods. The 3D analysis of mm-sized inclusions in chondrites achieves efficient partial extraction and high-precision isotopic analysis of irregularly shaped samples. This approach addresses gaps in existing cosmochemical data and broadens understanding of chemical and isotopic evolution of the early Solar System.

This short article is an essay with my opinion on the near-future direction of petrology and geochemistry, which has been shaped by my research experience on high-pressure metamorphic rocks in convergent boundaries, especially low-temperature eclogite. Subducted oceanic crust with basaltic chemical compositions transforms into eclogite around subarc depths with significant dehydration, thereby producing solute-bearing aqueous fluids. This type of eclogite samples are mines of information on fluid–rock interactions under high-pressure conditions, but it remains challenging to investigate submicron-scale mass-transfer processes, which I believe the fundamentals of the subduction-zone dynamics. The demand for in situ geochemical analyses will increase, and more comprehensive theories for fluid-involved physicochemical processes including metasomatism and rock deformation may be required. Research collaborations among multidisciplinary fields would facilitate discussion on this topic and vitalize the broad geoscience community.

Research on mantle materials is entering a transformative phase, driven by the rapid advancement of analytical techniques and a renewed focus on alteration processes of mantle materials. I present a mantle research strategy built on a different perspective. The concept itself is simple—to pursue the deepest accessible mantle materials beneath the ocean floor. Although direct access to mantle materials becomes progressively more difficult with depth, we overcame this limitation and achieved the world’s deepest recovery of oceanic mantle materials from the ocean floor. Based on these unprecedented samples, I outline my geochemical research strategy for the coming decade.

Geochemistry is a field of research built on efforts to describe and characterize the behavior of elements and molecules on the Earth. In geochemical studies, conventionally, the Goldschmidt classification has provided a conceptual framework for research strategies. This article revisits the Vernadsky classification and proposes a new classification into three categories: disperse elements, enriched elements, and phase-forming elements. Disperse elements in the Vernadsky classification are defined as elements which are contained in various minerals, and not major constituents of any particular mineral phase. In this article, disperse elements are further subdivided into disperse elements in the strict sense like germanium and enriched elements including rubidium. In contrast to disperse elements, major constituent elements of mineral phases are phase-forming elements. Geochemistry of disperse elements can provide key information for capturing a gradual change during the temporal evolution of geochemical systems, while geochemistry of phase-forming elements and enriched elements is advantageous for providing important information at a certain timing. In conventional geochemistry, due to the technical limitations in elemental and isotopic measurements, deep understanding of phase-forming elements and enriched elements are main subjects. With the recent advances in analytical chemistry, we should now attempt a systematic investigation of disperse elements.

In recent years, advances in microanalytical techniques have enabled high-spatial-resolution, multi-point measurements of chemical and isotopic compositions in rocks and minerals, resulting in a substantial expansion of geochemical data in both quality and quantity. This development is driving a shift from interpretations based on representative values toward research approaches that treat heterogeneity and diversity as data distributions. At the same time, challenges remain in the acquisition and effective utilization of large datasets, including the burden of sample preparation, the evaluation of uncertainty, and issues related to data management. In this paper, focusing on solid Earth geochemistry, I outline a research perspective aimed at expanding and effectively utilizing geochemical data from three viewpoints: acceleration and automation of experimental sample preparation, statistical data analysis that explicitly accounts for uncertainty, and high-dimensional data analysis based on open-access databases. Through collaboration with data science and mathematical statistics, these approaches are expected to enhance the interpretability of geochemical data and to contribute to the development of new insights and research questions.