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Constraining aplite-host granodiorite relationships through geochemistry and rhyolite-MELTS geobarometry: Tuolumne Intrusive Complex, Yosemite National Park (California, USA)

Marvin A. Lopez Acevedo1, Guilherme A. R. Gualda2, Calvin F. Miller2, Liam J. Kelly2, Elizabeth C. Teeter2

  • Affiliations: Fisk-Vanderbilt Masters-to-PhD Bridge Program, Nashville, TN, USA1; Department of Earth and Environmental Sciences, Vanderbilt University, Nashville, TN, USA2

  • Presentation type: Poster

  • Presentation time: Monday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 55

  • Programme No: 1.7.42

  • Theme 1 > Session 7

Abstract

The Tuolumne Intrusive Complex (TIC)--the youngest (90-82 Ma) igneous intrusion in Yosemite National Park--provides insights into magmatic processes. The TIC mostly comprises fine-to-coarse grained granodiorite. Aplite dikes are common within all units of the TIC. Aplites typically form during late-stage plutonism, forming dikes with distinct contacts with the host granodiorite. However, the temperature-pressures at which aplites formed and how they compare to those of host granodiorite at the TIC are not well constrained. Therefore, this study seeks to use rhyolite-MELTS geobarometry to estimate the depth at which aplite dike melts were extracted from host mush, and to test whether it differs from depths of emplacement of host rocks. Additionally, thin sections of aplite dikes and host rocks will be used to investigate the chemical and textural variability across related TIC units.  Fifteen aplite samples and five host rock samples were collected in October 2024. The thickness of the aplites ranges between ~1 cm and 30 cm, and they exhibit equigranular, 'sugary' textures. Many TIC aplites display both fine-grained and coarse-grained sections. In some samples, the transition from host rock to aplite is gradational, while in others, it is sharp. Some aplites contain feldspar megacrysts near or within the aplites. Whole-rock major element chemistry will be used to obtain chemical data of six aplite dikes and three granodiorite host rocks, providing critical input for geobarometry. Thin sections will complement thermodynamic simulations and aid in comparing aplites and host rocks from different units, and to evaluate aplite-granodiorite petrogenic relationships.