Presentation Information
[R8-P-03]Implication for fluid infiltration during retrograde metamorphism constrained by mode of occurrence of fracture-filling microcrystalline quartz and Al2SiO5 mineral assemblage: An example from the Sør Rondane Mountains, East Antarctica
*Fumiko HIGASHINO1, Tetsuo Kawakami1, Hayato Ikeda1, Tatsuro Adachi2, Masaoki Uno3 (1. Kyoto Univ., 2. Kyushu Univ., 3. Univ. Tokyo)
Keywords:
fibrolite,fibrous kyanite,fluid infiltration,acidic aqueous fluid
Fluid flow and diffusion cause mass transfer and reaction during metamorphism. Fibrolite is generally known as a variety of sillimanite (Al2SiO5), which appears like a branch of fibers in Al-rich pelitic rocks. Fibrolitic sillimanite often replaces and/or grows on prismatic Al2SiO5 minerals and biotite. [1] suggests high aHCl fluid enhanced late-stage fibrolitization of biotite. Fibrolite is also present in grain boundaries of feldspar, cordierite and garnet [2]. It is noted that previous studies often identify “fibrolitic sillimanite” based only on microscopic observation without using Raman spectroscopy. This study reports mode of occurrences of a fracture-filling microcrystalline quartz-Al2SiO5 mineral assemblage from the Sør Rondane Mountains (SRM), East Antarctica.
The SRM, which are mainly dominated by granulite facies gneisses and granitoids, are thought to be a part of the collision zone between East and West Gondwana during the East African-Antarctic Orogeny [3]. The timing of granulite facies metamorphism is 650-600 Ma, followed by retrograde metamorphism under andalusite stability field at 590-530 Ma [4].
This study reports mode of occurrences of a fracture-filling microcrystalline quartz-Al2SiO5 mineral assemblage. Sample descriptions are shown in [5] in detail. Such fractures are observed within plagioclase, K-feldspar and cordierite. The Al2SiO5 minerals often show polyphase assemblage and identified to be kyanite and fibrolitic sillimanite coexisting together in the same fracture by Raman spectroscopy. The microcrystalline quartz-Al2SiO5 mineral assemblage can be formed by acidic aqueous fluid infiltration which removed alkali and alkaline-earth metals in feldspars and cordierite. We will discuss the formation process of the microcrystalline Al2SiO5 minerals.
Reference [1] Kerrick 1987 Am. Min. [2] Vernon & Flood 1977 CMP [3] Meert 2003 Tectonophysics [4] Osanai et al. 2013 Precam. Res. [5] Higashino et al. 2025 Polar Sci.
The SRM, which are mainly dominated by granulite facies gneisses and granitoids, are thought to be a part of the collision zone between East and West Gondwana during the East African-Antarctic Orogeny [3]. The timing of granulite facies metamorphism is 650-600 Ma, followed by retrograde metamorphism under andalusite stability field at 590-530 Ma [4].
This study reports mode of occurrences of a fracture-filling microcrystalline quartz-Al2SiO5 mineral assemblage. Sample descriptions are shown in [5] in detail. Such fractures are observed within plagioclase, K-feldspar and cordierite. The Al2SiO5 minerals often show polyphase assemblage and identified to be kyanite and fibrolitic sillimanite coexisting together in the same fracture by Raman spectroscopy. The microcrystalline quartz-Al2SiO5 mineral assemblage can be formed by acidic aqueous fluid infiltration which removed alkali and alkaline-earth metals in feldspars and cordierite. We will discuss the formation process of the microcrystalline Al2SiO5 minerals.
Reference [1] Kerrick 1987 Am. Min. [2] Vernon & Flood 1977 CMP [3] Meert 2003 Tectonophysics [4] Osanai et al. 2013 Precam. Res. [5] Higashino et al. 2025 Polar Sci.