[S-CG45] Petrology, Mineralogy & Resource Geology

[SCG45-P06] Pressure-temperature estimation using melt inclusions in zircon from Daito granodiorite in the Un-nan area, San’in zone

Chiho Ihira², *Satoshi SAITO¹ (1.Graduate School of Science and Engineering, Ehime University, 2.Faculty of Science, Ehime University)

Keywords:Melt inclusions in zircon, Geothermobarometer, Daito granodiorite

In this study, we estimate crystallization pressures and temperatures of zircons using melt inclusion compositions in zircon, a ubiquitous accessory mineral in granitoids. Homogenization experiments of polymineralic inclusions hosted in zircon have been conducted for a granitoid sample from the Paleogene Daito granodiorite in San’in zone, southwest Japan, using a piston-cylinder high pressure–high–temperature apparatus. High SiO₂ contents (77–79 wt% anhydrous basis) of homogenized melt inclusions are revealed by SEM-EDS analysis implying that they represent fractionated interstitial melts trapped in growing zircon crystals. The MagMaTaB geothermobarometer (Weber and Blundy, 2024) applied for nine melt inclusion compositions yields pressures ranging from 452 to 161 MPa (with error of ± 100 MPa), interpreted as the crystallization pressures of zircons, implying that zircon crystallized at various pressures during magma ascent. Furthermore, the estimated temperatures (771–695 C with error of ± 25 C using the MagMaTaB geothermometer) show slight increase with decreasing pressures implying reheat of magma reservoir during ascent probably induced by injection of mafic magma into magma reservoir, which is consistent with field observation of abundant mafic magmatic enclaves in the Daito granodiorite. On the other hand, the rhyolite-MELTS geobarometer (Gualuda et al., 2014) yields pressures ranging from 170 to 49 MPa (with error of ± 25 MPa) for four of nine melt inclusion compositions. The results are consistent with field observations suggestive of a shallow intrusive level of the Daito granodiorite.