75-29 The Volcano Plutonic Connection — Zircon Petrochronology of the ~14 Ma Mt. Ishizuchi Caldera, Japan.

Session: Mineralogy, Geochemistry, Petrology, and Volcanology Student Session (Posters)

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Abstract:

The ~14 Ma Mt. Ishizuchi caldera, located in the Ehime province of Shikoku Island, is an eroded caldera complex that reveals bodies of volcanic and plutonic rocks. Understanding the relationships between plutonic and volcanic rocks in caldera systems is vital for obtaining insight into silicic magma systems and their lifetime durations. Recognizing these systems enhances our knowledge of the processes involved in the formation of Earth’s crust. This study utilizes uranium-lead (U-Pb) zircon chronology to test the hypothesis that the plutonic and volcanic rocks are coeval and consanguineous by identifying chemical and chronological relationships between the rocks of the Ishizuchi caldera. Zircon from volcanic and plutonic samples of the Ishizuchi caldera was analyzed for U-Pb ages and trace elements using LA-ICP-MS. The four samples include volcanic rocks from the Takano dacite and Tengudake Tuff, and plutonic rocks from the Saksegawa granodiorite and Teppouishigawa adamellite. Geochronological results from zircons in plutonic rocks range from 12.5 ± 0.98 Ma to 15 ± 1.3 Ma. Zircons in volcanic rocks range from 12.8 ± 1.6 Ma to 15.1 ± 0.87 Ma. Ti-in-zircon crystallization temperatures of plutonic and volcanic rocks range from 775 – 990 °C, but are not correlated with trace element geochemistry. Rather, zircons of the Takano dacite and Saksegawa granodiorite show lower degrees of melt evolution (Eu/Eu*: 0.12 – 0.025) than the Tengudake tuff and Teppouishigawa adamellite (Eu/Eu*: 0.05 – 0.02). Petrochronologic results demonstrate the intricate consanguinity of these coeval caldera lithologies and that their genesis took place over multiple cooling events that span 2.5 Ma.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10084

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