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Development of a quartz-based geothermometer for biogenic chert
Haruka Tanaka1, Sharav Davaanyam2, Bayart Nadmid1
1Graduate School of Environmental Studies, Nagoya University, Nagoya, 464-8601, Japan.
Scientific Reports
|November 29, 2025
Summary
Researchers developed a new quartz-based geothermometer using quartz crystallinity (CI) and grain size (GS) to estimate diagenetic/metamorphic temperature (PT) in biogenic chert. This method enhances tectonic studies in areas with limited erosion.
Area of Science:
- Geology and Tectonics
- Geochemistry
- Paleontology
Background:
- Estimating diagenetic/metamorphic temperature (PT) is challenging in inactive erosion areas where only biogenic chert is exposed.
- Biogenic chert, formed from amorphous silica in sediments, undergoes changes in quartz crystallinity (CI) and grain size (GS) during diagenesis/metamorphism.
- The precise relationship between CI, GS, and PT in biogenic chert requires further exploration for reliable geothermometry.
Purpose of the Study:
- To investigate the correlation between quartz crystallinity (CI), grain size (GS), and diagenetic/metamorphic temperature (PT) in biogenic chert.
- To develop a novel quartz-based geothermometer for estimating PT in tectonically significant regions.
- To advance understanding of diagenetic and metamorphic processes in accretionary complexes.
Main Methods:
- Analysis of Paleozoic-Mesozoic biogenic chert and metachert samples from four distinct regions in East Asia.
- Systematic examination of the relationships between quartz crystallinity (CI) and grain size (GS) across varying diagenetic/metamorphic temperatures (PT).
- Statistical correlation analysis to establish the reliability of CI and GS as geothermometers.
Main Results:
- A consistent, systematic relationship was identified between CI, GS, and PT in biogenic chert across diverse geological settings.
- In cryptocrystalline chert (GS ≤ 1.94 μm), CI and GS show a strong logarithmic correlation. In crystalline chert, CI plateaus while GS varies widely.
- Both CI and GS demonstrate strong positive correlations with increasing PT (R > 0.929), with linear and logarithmic trends respectively.
Conclusions:
- Quartz crystallinity (CI) and grain size (GS) are reliable indicators for estimating diagenetic/metamorphic temperature (PT) in biogenic chert.
- The developed quartz-based geothermometer provides a valuable tool for tectonic studies in regions where traditional thermometry is difficult.
- Findings are consistent across different geological ages and locations, highlighting the universal applicability of this geothermometric approach.
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