Japan Geoscience Union Meeting 2024

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[J] Poster

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG46] New Insights of Fluid-Rock Interactions: From Surface to Deep Subduction Zone

Tue. May 28, 2024 5:15 PM - 6:45 PM Poster Hall (Exhibition Hall 6, Makuhari Messe)

convener:Atsushi Okamoto(Graduate School of Environmental Studies), Jun Muto(Department of Earth Sciences, Tohoku University), Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Junichi Nakajima(Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

5:15 PM - 6:45 PM

[SCG46-P17] Evaluation of reactive surface area during weathering of granite: an example of Mt. Gagara, Hiroshima

*Hikaru Okamura1, Tadashi Yokoyama2, Masahiro Kaibori3 (1.Hiroshima University, School of Integrated Arts and Sciences, 2.Hiroshima University, Graduate School of Advanced Science and Engineering, 3.Hiroshima University, Resilience Research Center)

Keywords:Granite, Weathering, Reactive transport modeling, Reactive surface area

Granites are widely distributed in Chugoku district, Japan. Saprolite is formed as a result of weathering of granite. Granites are mainly composed of quartz, plagioclase, K-feldspar and biotite, and each of which has different resistance to weathering. In this study, we examined how the reactive surface area (surface roughness) of minerals in granite from Mt. Gagara, Hiroshima, changes as weathering progresses. Borehole cores of Mt. Gagara, drilled to a depth of 20 meters from the ground surface, were analyzed. Dissolution experiments were conducted on unweathered (UNW) and strongly weathered (W-3B) rock samples and concentrations of dissolved elements were measured. In addition, numerical simulations of rock dissolution were performed using PHREEQC (Parkhurst and Appelo, 2013). By comparing the calculated results with the experimental results, the surface roughnesses of minerals were evaluated. The results showed that the surface roughnesses of plagioclase and K-feldspar in W-3B were significantly greater than those in UNW. The interior of neither Plagioclase nor K-feldspar is homogeneous, and there are differences in composition within a single grain. The resistance to weathering depends on their composition. In W-3B, areas of low resistance to weathering inside plagioclase and K-feldspar may have already been lost due to weathering. Therefore, water may have penetrated inside the plagioclase and K-feldspar in W-3B, causing dissolution, resulting in greater surface roughness in W-3B compared to those in UNW.