Low-aTiO₂ in rhyolitic magma for the Kinpusan pluton case, central Japan

Abstract

Ti-in-zircon geothermometry is widely applied to silicic magmas. However, reliable temperature estimates depend on the activity of TiO₂ in the melt relative to rutile saturation (aTiO₂), which may change significantly during magma crystallization. We constrain realistic aTiO₂ values for high-silica rhyolitic magmas by integrating Ti concentration measurement in zircon with thermodynamic modeling of the Miocene Kinpusan granite, a shallow intrusion emplaced at ∼ 50 MPa in central Japan. Zircons show uniformly low Ti contents (interquartile range of ∼ 2.0-4.5 µg/g). MAGEMin phase-equilibrium modeling combined with zircon saturation calculations indicates that zircon saturation occurs at <800 °C and melt fractions ≤90 vol%. Within the zircon-melt coexistence interval (∼ 750-800 °C), both thermodynamic predictions and the observed Ti concentrations in zircon require low aTiO₂ values of ∼ 0.1-0.4, consistent with the petrographic absence of rutile and ilmenite. The models also predict a sharp increase in Ti concentration in zircon immediately above the solidus, implying that the highest Ti contents reflect eutectic crystallization. These results also support the idea that aTiO₂ must vary during crystallization and cannot be assumed constant in a rhyolitic magma system.

INTRODUCTION

Temperature is one of the most fundamental parameters governing crustal processes, including magmatism and metamorphism. Geothermometries based on titanium (Ti) in quartz and zircon, which has rapidly gained widespread use in the past two decades, are now a mainstream technique for estimating crystallization temperatures (Watson and Harrison, 2005; Watson et al., 2006; Wark and Watson, 2006; Ferry and Watson, 2007; Huang and Audétat, 2012; Crisp et al., 2023; Kirkpatrick et al., 2025). A persistent limitation of existing applications, however, lies in the treatment of the activity of TiO₂ relative to rutile saturation (aTiO₂; Ghent and Stout, 1984). In many studies, aTiO₂ has been assumed based on the presence or absence of Ti-bearing mineral phases in the analyzed samples; for example, aTiO₂ is often assumed to be 0.7-1 in rutile-absent but titanite-bearing systems, and 0.5 when ilmenite is present (e.g., Schiller and Finger, 2019; Carter and Williamson, 2022). Watson and Harrison (2005) and Hayden and Watson (2007) further suggested that most natural silicate melts capable of crystallizing zircon are characterized by aTiO₂ > 0.5.

Recent work has demonstrated that aTiO₂ is not constant but a dynamic variable that evolves with temperature, mineral assemblage, and the TiO₂ budget of the melt (Fonseca Teixeira et al., 2024). Thermodynamic modeling tools such as the MELTS family (e.g., Gualda et al., 2012) can be used to explore such variability, yet in rhyolitic systems these programs often predict much lower aTiO₂ values (<0.3) than expected from other thermometric constraints (e.g., Fe-Ti oxide thermometry). This discrepancy complicates the application of Ti-in-zircon geothermometry to rhyolitic systems (Kularatne and Audétat, 2014; Fonseca Teixeira et al., 2024).

In this study, we constrain feasible ranges of aTiO₂ for rhyolitic magmas by integrating Ti concentrations in zircon with crystallization temperatures derived from quasi-eutectic melt compositions of the Kinpusan granite, central Japan. This approach allows us to evaluate and validate the low aTiO₂ values predicted for shallow rhyolitic magma systems.

GEOLOGICAL SETTING

We examined samples from the Miocene Kinpusan granite, which intrudes the Cretaceous accretionary complex in the Kanto Mountains, central Japan (Fig. 1A; Saito et al., 2007). The pluton exhibits a well-developed layered structure with alternating felsic magmatic enclave (FME)-bearing and FME-free units. This layering is interpreted to reflect incremental emplacement of discrete magma batches (Takahashi et al., 2021). Its high-silica rhyolitic composition and the abundance of miarolitic cavities indicate emplacement at very shallow crustal levels (Candela, 1997; Gualda and Ghiorso, 2013). The Kinpusan granite is characterized by a dominant porphyritic texture, with well-developed graphic intergrowths occurring both within the groundmass and at the rims of phenocrysts. Modal measurements of phenocrysts show that the magma had crystallized to about 14-30 vol% prior to intrusion (Yamaoka et al., 2025). Ilmenite is exceedingly rare and rutile is absent in the granite (Sawaki et al., 2020).

Figure 1. (A) Geological overview and locality of samples around the Kinpusan pluton, after Yamaoka et al. (2025). (B) Bulk-rock CIPW normative compositions of aplite and host granite of the Kinpusan pluton projected onto the quartz (Qtz)-orthoclase (Or)-albite (Ab) ternary diagram, with showing minimum and eutectic melt compositions at a range of pressures (MPa) after Blundy and Cashman (2001). Bulk-rock analyses are converted to CIPW norms and corrected for the anorthite content following Blundy and Cashman (2001). Granite data are from Kato (1968a, 1968b), Saito et al. (2007), and Takahashi et al. (2021).

ANALYTICAL METHODS

XRF analysis of aplite

To constrain melt compositions at the time of emplacement, we employed bulk compositions of aplite sills interpreted as segregated melt fractions extracted from the host granite at emplacement depth (Yamaoka et al., 2025). Whole-rock major element compositions of aplite samples were analyzed by X-ray fluorescence spectrometry (XRF) using the glass bead method. Rock samples were crushed to powder using a tungsten carbide mill. Approximately 0.5 g of dried powder—pre-heated at >110 °C for ∼ 12 h and subsequently ignited at 950 °C for 2 h—was mixed with 5.0 g of lithium tetraborate flux and fused to produce glass beads. The mass difference before and after ignition was taken as the loss on ignition (LOI). Major element concentrations were measured using a PANalytical Axios XRF spectrometer at the Geological Survey of Japan (GSJ). Calibration lines for each element were constructed using 17 GSJ rock reference materials (JA-1, JA-2, JA-3, JB-1a, JB-1b, JB-2, JB-3, JF-1, JF-2, JG-1a, JG-2, JG-3, JGb-1, JP-1, JR-1, JR-2, and JR-3). Results are listed in Supplementary Table S1 (Supplementary Tables S1-S3 are available online from https://doi.org/10.2465/jmps.260129).

Sample description and LA-ICP-MS analysis of zircon

Zircon grains from three granite samples previously dated by U-Pb geochronology (KPC-16, KPD-25, KPI-13; Yamaoka et al., 2025) were used for Ti quantification. All granite samples show a porphyritic texture and contain euhedral phenocrysts of quartz, plagioclase, and alkali feldspar, with minor biotite phenocrysts measuring 2-4 mm. Minerals in the groundmass are similar to the phenocryst and are anhedral. Micrographic texture is characterized by intergrowths of quartz and alkali feldspar. In all samples, part of the biotite is chloritized and alkali feldspar is weakly sericitized. Zircon, apatite, allanite, monazite, and magnetite are recognized as accessory minerals. In all samples, zircon is only present in groundmass part. Cathodoluminescence images of analyzed zircon grains consistently show oscillatory zoning lacking core-rim distinctions, indicating crystallization during a single magmatic event without major compositional perturbation (Fig. S29 in Yamaoka et al., 2025). Except for one grain in KPC-16, which yields a Cretaceous igneous age and is therefore interpreted as xenocrystic, all zircons record tightly constrained crystallization ages of 15.1-15.0 Ma (Yamaoka et al., 2025). Thirty spots—one per grain, including the grain cores—were analyzed across the three samples using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) at AIST.

Ti concentrations in zircon were measured by LA-ICP-MS (Raijin α, Seishin Trading Co., Ltd.; Agilent 8900 ICP-QQQ, Agilent Technologies) at the GSJ. The LA-ICP-MS analytical conditions are summarized in Supplementary Table S2. Titanium was measured in O₂ reaction gas MS/MS mode using a mass-shift approach (Q1 = 48; Q2 = 64) to suppress spectral interference from ⁹⁶Zr²⁺ (Table S2). Data reduction, including background subtraction, internal-standard normalization, external calibration, and calculation of elemental concentrations, was performed using an in-house Microsoft Excel VBA script.

Elemental compositions were quantified using ²⁹Si as an internal standard to correct for variations in signal intensity among individual samples. For each element, calibration was performed by plotting, on the y-axis, the product of the signal intensity ratio (analyte/²⁹Si) and the content of the internal standard, against the analyte concentration on the x-axis. Calibration lines were established using NIST SRM 610 glass as the primary reference material for P, Ti, Sr, and Y (Jochum et al., 2011). Zr and Hf were calibrated using natural zircon (Harvard 91500: Zr, 152800 µg/g; Hf, 5895 µg/g; Wiedenbeck et al., 2004). Provisional elemental compositions were calculated by assuming a Si content of 15.3 wt% in the sample and were then normalized so that the total oxide abundance of all measured elements sums to 100 wt%. The mean of Ti contents of 91500 zircon (4.77 ± 0.21 µg/g, 95% confidence level) is consistent with their recommended values (4.73 ± 0.15 µg/g, 95% confidence level; Szymanowski et al., 2018). Results of the analysis are listed on Supplementary Table S3.

Thermodynamic modeling

The Mineral Assemblage Gibbs Energy Minimization (MAGEMin) thermodynamic package (MAGEMin_C version 2.1.5; Riel et al., 2022) was used to calculate stable phase equilibria at given P-T-X (pressure-temperature-composition) conditions in the K₂O-Na₂O-CaO-FeO-MgO-Al₂O₃-SiO₂-H₂O-TiO₂-Fe₂O₃ system, with igneous thermodynamic database ds636 provided by Green et al. (2025), corrected after Holland et al. (2018). This database allows simulations at temperatures around the solidus and in mineral assemblages involving biotite and amphibole—conditions that are difficult to model accurately with rhyolite-MELTS (Gualda and Ghiorso, 2013). Calculations were performed using the following solution models: ilmenite, garnet, orthopyroxene from Weller et al. (2024), feldspar from Holland et al. (2022), biotite, fluid, silicate melt from Green et al. (2025), amphibole from Green et al. (2016), and spinel from Tomlinson and Holland (2021). The primary bulk composition used for calculations is MAS-02 from Saito et al. (2007), which reflects the average rhyolitic composition of the pluton. Sawaki et al. (2022) report a consistent dominance of magnetite over ilmenite in the Kinpusan granite as surrounding contemporaneous granites, leading to the selection of ΔQFM buffer values of +2 log unit (Ishihara, 1977). The presence of ilmenite and the absence of magnetite in the modeling results are inconsistent with petrographic observations (Supplementary Fig. S1A; Fig. S1 is available online from https://doi.org/10.2465/jmps.260129). However, these phases are not significantly saturated at temperatures above the solidus and therefore do not affect the conclusions. All modeling assumes water saturated conditions in the considered pressure-temperature space. Variations in H₂O content do not affect the conclusion, except in cases with extremely dry conditions lower than 1 wt% in a system (Fig. S1B).

To evaluate zircon saturation conditions, MAGEMin-derived melt compositions and melt-crystal partition coefficients (bulk D values from Laurent, 2012) were combined with the zircon saturation model of Crisp and Berry (2022), following the approach of Barboni and Schoene (2014). Although MAS-02 contains 84 µg/g Zr, we also tested the maximum reported value (110 µg/g; Saito et al., 2007) to assess the potential effect of sampling bias on zircon saturation temperature.

RESULTS

Emplacement depth

The whole-rock chemical compositions of the Kinpusan granite from literature exhibit no systematic variation within the pluton and consistently fall within the high-silica rhyolite field, with SiO₂ contents of 75-78 wt% (Kato, 1968a, 1968b; Saito et al., 2007; Takahashi et al., 2021). Such compositions are compatible with melt segregation at pressures <300 MPa (Gualda and Ghiorso, 2013). In contrast, the aplite sills display a narrower compositional range, with SiO₂ contents of 77-78 wt% (Table S1). Their CIPW normative compositions—calculated following the anorthite correction of Blundy and Cashman (2001)—are plotted around a cotectic line at 50 MPa toward more norm quartz-rich compositions relative to the host granite on the quartz (Qtz)-orthoclase (Or)-albite (Ab) ternary diagram (Fig. 1B). This show that the aplite melt extraction and segregation occurred after emplacement of the pluton at ∼ 50 MPa.

Measured Ti concentrations in zircon

Ti concentrations in zircon from the three samples exhibit highly consistent patterns. Maximum values remain below 7 µg/g, and the interquartile range (IQR) spans ∼ 2.0-4.5 µg/g (Fig. 2A). Median concentrations fall between 2.5 and 3.2 µg/g. Because mean values are consistently ∼ 0.3-0.6 µg/g higher than the medians, the distributions display a slight positive skew, with a longer tail toward higher Ti concentrations (Fig. 2A). A similar distributional pattern is observed in the 69 analyses of Ti concentration in zircon reported by Sawaki et al. (2022) for six samples (GR20, GR17, GR29, KNP2, GR072, and GR076), which yield slightly low or comparable IQRs of ∼ 1.4-3.1 µg/g (Fig. 2A).

Figure 2. (A) Box-and-whisker plots of Ti concentrations in zircon. The dataset of Sawaki et al. (2022) is a compilation of 69 analyses from six samples collected in the Mizugaki-Shosenkyo bodies. (B) Relationship between Ti concentrations in zircon and temperature based on solubility models of Ferry and Watson (2007) and Crisp et al. (2023).

Modeled zircon saturation and aTiO₂

Model calculations using MAGEMin elucidate the relationship between the crystallization path in P-T space and zircon saturation (Figs. 3A and S1). Across 1-200 MPa, magmas that have crystallized by around 10 vol% (i.e., melt fraction X_m = 0.9) reach the solidus after only ∼ 30-80 °C of cooling. Zircon saturation lines exhibit negatively sloped but near-isothermal trajectories in P-T space, and at pressures below 100 MPa, zircon saturation is achieved at temperatures near 800 °C. At 50 MPa, zircon stability in the presence of melt is confined to a narrow temperature interval. For the bulk Zr concentration (C_Zr) = 84 µg/g, zircon saturation begins at ∼ 780 °C and continues to the solidus at ∼ 750 °C, whereas for C_Zr = 110 µg/g, the onset of saturation shifts upward to ∼ 800 °C. In both cases, initial zircon saturation occurs when the melt fraction has decreased to ≤90 vol% (Fig. 3A). Across most melt-bearing conditions, aTiO₂ remains below 0.2 and then rises sharply to ∼ 0.5 within a few degrees of the solidus (Figs. 3A and 3B). Below the solidus, aTiO₂ increases further to around 0.5 as ilmenite approaches or attains saturation. The activity of silica (aSiO₂) remains close to 1 throughout the modeled P-T space, except at higher temperatures (∼ 900 °C), where it decreases slightly to ∼ 0.9 (Fig. 3C).

Figure 3. (A) aTiO₂, melt fraction, and zircon saturation conditions in the P-T space calculated using MAGEMin for Kinpusan granite (composition: MAS-02 in Saito et al., 2007). Detailed model settings are described in the main text. X_m: melt fraction. C_Zr: bulk Zr concentration. (B), (C) aTiO₂ and aSiO₂ variation with temperature at 50 MPa. (D) Ti concentration in zircon predicted using the solubility models of Ferry and Watson (2007) and Crisp et al. (2023). The gray shaded area on A to D represents the temperature range over which zircon saturation is achieved in the Kinpusan magma, assuming a conservative scenario corresponding to the highest whole-rock Zr concentration (C_Zr = 110 µg/g).

Range of aTiO₂ in the Kinpusan granite magma system

Within the temperature interval of ∼ 750-800 °C, where zircon can stably coexist with silicate melt, aTiO₂ must be consistent with the measured Ti concentrations in zircon under values assuming thermodynamic equilibrium. As illustrated in Figure 2B, lower Ti concentration in zircon require correspondingly lower aTiO₂. Using the calibration of Crisp et al. (2023), Ti concentrations in zircon below 7 µg/g imply aTiO₂ values of ∼ 0.5 or lower within this temperature range. In this framework, the observed IQR of ∼ 2.0-4.5 µg/g for zircons from the Kinpusan granite corresponds to low aTiO₂ values of ∼ 0.1-0.3 (Fig. 2B). Application of the Ferry and Watson (2007) calibration yields similarly low results, requiring aTiO₂ values below ∼ 0.4 (Fig. 2B).

DISCUSSION

Reliability of Ti concentrations in zircon

In general, laser ablation spots used for measuring Ti concentrations in zircon are typically 20-30 µm in diameter and commonly transect several zoning domains that are recognizable in CL images. As a result, the measured Ti concentrations often represent spatially averaged values. This caveat also applies to this study. Ti concentrations in zircon is highly resistant to diffusive re-equilibration under crustal conditions (Watson et al., 2006; Cherniak, 2010). Therefore, the Ti concentrations measured in zircons in this study can be interpreted as recording some temperatures spanning from zircon saturation to solidus conditions.

Evidence for low aTiO₂

Application of the Ti concentration measurements in zircon to Ti-solubility models indicates that low aTiO₂ values (0.1-0.3) under near-solidus to hyper-solidus conditions are required to satisfy the crystallization-temperature constraints. Such low aTiO₂ values are independently reproduced by the MAGEMin modeling, lending support to the thermodynamic results. Similarly low aTiO₂ values were reported as exceptional case by Schiller and Finger (2019) (samples Nos. 12-14). These samples exhibit consistently low TiO₂/Zr ratios (<0.0015) and ilmenite-poor features, comparable to those of the Kinpusan granite compositions (Saito et al., 2007). Therefore, the inferred low aTiO₂ can be interpreted to result from the absence of ilmenite-zircon paragenesis during magma crystallization under strongly TiO₂-undersaturated conditions.

Implications for Ti-in-zircon geothermometry application

At the emplacement P-T conditions estimated from MAGEMin (50 MPa; ∼ 750-800 °C), the aTiO₂ values predicted by the calibration of Crisp et al. (2023) imply a steep rise in Ti concentration near the solidus—from ∼ 3.5-4 µg/g to ∼ 7 µg/g above ∼ 760 °C (Fig. 3D). The calibration of Ferry and Watson (2007) exhibits the same trend but yields absolute concentrations that are 1-1.5 µg/g lower. These calculations suggest that the higher Ti concentrations exceeding the interquartile range (>4.5 µg/g) observed in the analyzed zircons likely reflect crystallization under elevated aTiO₂ conditions within a limited temperature interval close to the solidus. Such elevated aTiO₂ is likely a consequence of a sharp increase in TiO₂ concentration in the melt during the cotectic crystallization of feldspar and quartz. (Fonseca Teixeira et al., 2024). Therefore, assuming a constant aTiO₂ in Ti-in-zircon geothermometry would invert the expected relationship between Ti concentration and temperature, leading to erroneous reconstructions of zircon crystallization timing and the thermal evolution of the magma. In rhyolitic magma systems, higher Ti concentrations in zircon rims relative to cores are often interpreted as evidence of recharge events in a magma chamber (e.g., Claiborne et al., 2010; Chen et al., 2021). However, our case emphasizes that the high-Ti zircon rims sometimes may also form during simple closed-system cooling and crystallization, and therefore should not necessarily be regarded as direct diagnostic evidence of magma recharge.

ACKNOWLEDGMENTS

We thank Takashi Kudo for valuable assistance with the XRF analysis. Members of Kyoto Fission-Track Co. Ltd. are also thanked for the preparation of the zircon-mounted sample used for Ti content measurements. This work was supported by JSPS Grant-in-Aid for Scientific Research JP23K19076 and the Japan Science and Technology Agency SPRING, Japan, Grant Number JPMJSP2144 (Shinshu University). We are grateful to Shumpei Yoshimura for careful handling of the manuscript. Constructive comments from Shunsuke Endo, Takashi Hoshide, and an anonymous reviewer helped greatly to improve the manuscript.

SUPPLEMENTARY MATERIALS

Supplementary Tables S1-S3 and Figure S1 are available online from https://doi.org/10.2465/jmps.260129.

REFERENCES

•  Barboni,  M. and  Schoene,  B. (2014) Short eruption window revealed by absolute crystal growth rates in a granitic magma. Nature Geoscience, 7, 524-528.
•  Blundy,  J. and  Cashman,  K. (2001) Ascent-driven crystallisation of dacite magmas at Mount St Helens, 1980-1986. Contributions to Mineralogy and Petrology, 140, 631-650.
•  Candela,  P.A. (1997) A review of shallow, ore-related granites: textures, volatiles, and ore metals. Journal of Petrology, 38, 1619-1633.
•  Carter,  L.C. and  Williamson,  B.J. (2022) Textural indicators of mineralisation potential in porphyry magmatic systems — A framework from the archetypal Yerington district, Nevada. Ore Geology Reviews, 143, 104783.
•  Chen,  S.-R.,  Wang,  Q.,  Zhu,  D.-C.,  Weinberg,  R.F., et al (2021) Reheating and magma mixing recorded by zircon and quartz from high-silica rhyolite in the Coqen region, southern Tibet. American Mineralogist, 106, 112-122.
•  Cherniak,  D.J. (2010) Diffusion in accessory minerals: Zircon, titanite, apatite, monazite and xenotime. Reviews in Mineralogy and Geochemistry, 72, 827-869.
•  Claiborne,  L.L.,  Miller,  C.F. and  Wooden,  J.L. (2010) Trace element composition of igneous zircon: a thermal and compositional record of the accumulation and evolution of a large silicic batholith, Spirit Mountain, Nevada. Contributions to Mineralogy and Petrology, 160, 511-531.
•  Crisp,  L.J. and  Berry,  A.J. (2022) A new model for zircon saturation in silicate melts. Contributions to Mineralogy and Petrology, 177, 71.
•  Crisp,  L.J.,  Berry,  A.J.,  Burnham,  A.D.,  Miller,  L.A. and  Newville,  M. (2023) The Ti-in-zircon thermometer revised: The effect of pressure on the Ti site in zircon. Geochimica et Cosmochimica Acta, 360, 241-258.
•  Ferry,  J.M. and  Watson,  E.B. (2007) New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers. Contributions to Mineralogy and Petrology, 154, 429-437.
•  Fonseca Teixeira,  L.M.,  Troch,  J. and  Bachmann,  O. (2024) The dynamic nature of aTiO₂: Implications for Ti-based thermometers in magmatic systems. Geology, 52, 92-96.
•  Ghent,  E.D. and  Stout,  M.Z. (1984) TiO₂ activity in metamorphosed pelitic and basic rocks: principles and applications to metamorphism in southeastern Canadian Cordillera. Contributions to Mineralogy and Petrology, 86, 248-255.
•  Green,  E.C.,  Holland,  T.J.B.,  Powell,  R.,  Weller,  O.M. and  Riel,  N. (2025) Corrigendum to: Melting of Peridotites through to Granites: a Simple Thermodynamic Model in the System KNCFMASHTOCr, and, a Thermodynamic Model for the Subsolidus Evolution and Melting of Peridotite. Journal of Petrology, 66, egae079.
•  Green,  E.C.R.,  White,  R.W.,  Diener,  J.F.A.,  Powell,  R., et al (2016) Activity-composition relations for the calculation of partial melting equilibria in metabasic rocks. Journal of Metamorphic Geology, 34, 845-869.
•  Gualda,  G.A.R.,  Ghiorso,  M.S.,  Lemons,  R.V. and  Carley,  T.L. (2012) Rhyolite-MELTS: a modified calibration of MELTS optimized for silica-rich, fluid-bearing magmatic systems. Journal of Petrology, 53, 875-890.
•  Gualda,  G.A.R. and  Ghiorso,  M.S. (2013) Low-pressure origin of high-silica rhyolites and granites. The Journal of Geology, 121, 537-545.
•  Hayden,  L.A. and  Watson,  E.B. (2007) Rutile saturation in hydrous siliceous melts and its bearing on Ti-thermometry of quartz and zircon. Earth and Planetary Science Letters, 258, 561-568.
•  Holland,  T.J.B.,  Green,  E.C.R. and  Powell,  R. (2018) Melting of Peridotites through to Granites: A Simple Thermodynamic Model in the System KNCFMASHTOCr. Journal of Petrology, 59, 881-900.
•  Holland,  T.J.B.,  Green,  E.C.R. and  Powell,  R. (2022) A thermodynamic model for feldspars in KAlSi₃O₈-NaAlSi₃O₈-CaAl₂Si₂O₈ for mineral equilibrium calculations. Journal of Metamorphic Geology, 40, 587-600.
•  Huang,  R. and  Audétat,  A. (2012) The titanium-in-quartz (TitaniQ) thermobarometer: A critical examination and re-calibration. Geochimica et Cosmochimica Acta, 84, 75-89.
•  Ishihara,  S. (1977) The magnetite-series and ilmenite-series granitic rocks. Mining Geology, 27, 293-305.
•  Jochum,  K.P.,  Weis,  U.,  Stoll,  B.,  Kuzmin,  D., et al (2011) Determination of Reference Values for NIST SRM 610-617 Glasses Following ISO Guidelines. Geostandards and Geoanalytical Research, 35, 397-429.
•  Kato,  Y. (1968a) Petrology of the Tertiary Granitic Rocks around Kofu Basin, Central Japan. Science Report of the Tohoku University, 10, 241-312.
•  Kato,  Y. (1968b) On the Tertiary granitic rocks around Kohu basin, Yamanashi Prefecture. The Journal of the Japanese Association of Mineralogists, Petrologists and Economic Geologists, 59, 21-39.
•  Kirkpatrick,  H.M.,  Trail,  D.,  Harrison,  T.M. and  Bell,  E.A. (2025) Investigating pressure effects of Ti and Zr partitioning into zircon, quartz, and rutile at crustal temperatures. Chemical Geology, 673, 122518.
•  Kularatne,  K. and  Audétat,  A. (2014) Rutile solubility in hydrous rhyolite melts at 750-900°C and 2 kbar, with application to titanium-in-quartz (TitaniQ) thermobarometry. Geochimica et Cosmochimica Acta, 125, 196-209.
• Laurent, O. (2012) Les changements géodynamiques à la transition Archéen-Protérozoïque: étude des granitoïdes de la marge Nord du craton du Kaapvaal (Afrique du Sud). Sciences de la Terre. Université Blaise Pascal - Clermont-Ferrand II, 2012. Français.
•  Riel,  N.,  Kaus,  B.J.P.,  Green,  E.C.R. and  Berlie,  N. (2022) MAGEMin, an Efficient Gibbs Energy Minimizer: Application to Igneous Systems. Geochemistry, Geophysics, Geosystems, 23, e2022GC010427.
•  Saito,  S.,  Arima,  M.,  Nakajima,  T.,  Misawa,  K. and  Kimura,  J. (2007) Formation of Distinct Granitic Magma Batches by Partial Melting of Hybrid Lower Crust in the Izu Arc Collision Zone, Central Japan. Journal of Petrology, 48, 1761-1791.
•  Sawaki,  Y.,  Asanuma,  H.,  Abe,  M. and  Hirata,  T. (2020) U-Pb ages of granitoids around the Kofu basin: Implications for the Neogene geotectonic evolution of the South Fossa Magna region, central Japan. Island Arc, 29, e12361.
•  Sawaki,  Y.,  Asanuma,  H.,  Sakata,  S.,  Abe,  M. and  Ohno,  T. (2022) Trace-element composition of zircon in Kofu and Tanzawa granitoids, Japan: Quantitative indicator of sediment incorporated in parent magma. Island Arc, 31, e12455.
•  Schiller,  D. and  Finger,  F. (2019) Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions. Contributions to Mineralogy and Petrology, 174, 51.
•  Szymanowski,  D.,  Fehr,  M.A.,  Guillong,  M.,  Coble,  M.A., et al (2018) Isotope-dilution anchoring of zircon reference materials for accurate Ti-in-zircon thermometry. Chemical Geology, 481, 146-154.
• Takahashi, M., Nihira, S. and Kanamaru, T. (2021) Geology and emplacement mechanism of Kinpusan granitic pluton, Central Japan. Proceedings of the Institute of Natural Sciences, Nihon University, 56, 39-68 (in Japanese with English abstract).
•  Tomlinson,  E.L. and  Holland,  T.J.B. (2021) A thermodynamic model for the subsolidus evolution and melting of peridotite. Journal of Petrology, 62, egab012.
•  Wark,  D.A. and  Watson,  E.B. (2006) TitaniQ: A titanium-in-quartz geothermometer. Contributions to Mineralogy and Petrology, 152, 743-754.
•  Watson,  E.B. and  Harrison,  T.M. (2005) Zircon thermometer reveals minimum melting conditions on earliest earth. Science, 308, 841-844.
•  Watson,  E.B.,  Wark,  D.A. and  Thomas,  J.B. (2006) Crystallization thermometers for zircon and rutile. Contributions to Mineralogy and Petrology, 151, 413-433.
•  Weller,  O.M.,  Holland,  T.J.B.,  Soderman,  C.R.,  Green,  E.C.R., et al (2024) New Thermodynamic Models for Anhydrous Alkaline-Silicate Magmatic Systems. Journal of Petrology, 65, egae098.
•  Wiedenbeck,  M.,  Hanchar,  J.M.,  Peck,  W.H.,  Sylvester,  P., et al (2004) Further Characterisation of the 91500 Zircon Crystal. Geostandards and Geoanalytical Research, 28, 9-39.
•  Yamaoka,  K.,  Murakami,  D.,  Mori,  H.,  Morohoshi,  T., et al (2025) Emplacement and cooling history of a pluton with evident laminated structure constrained by field anatomy of the Kinpusan pluton, central Japan. Island Arc, 34, e70014.