Pyroxene exsolution in mafic granulites from the Grove Mountains, East Antarctica: constraints on Pan-African metamorphic conditions

• Published in: European Journal of Mineralogy
• Main Authors: Liu, XC, Zhao, ZR, Zhao, Y, Chen, J, Liu, XH
• Other Authors: Liu, XC (reprint author), Chinese Acad Geol Sci, Inst Geomech, Beijing 100081, Peoples R China., Chinese Acad Geol Sci, Inst Geomech, Beijing 100081, Peoples R China., Chinese Acad Geol Sci, Inst Geol, Beijing 100037, Peoples R China., Peking Univ, Elect Microscopy Lab, Beijing 100871, Peoples R China., Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China.
• Format: Journal/Newspaper
• Language: English
• Published: european journal of mineralogy 2003
• Subjects: pyroxene exsolution; inverted pigeonite; mafic granulite; metamorphic conditions; Pan-African; Grove Mountains; OPTIMAL PHASE BOUNDARIES; LARSEMANN-HILLS; EXPERIMENTAL CALIBRATION; CRUSTAL EVOLUTION; HIGH-TEMPERATURE; ENDERBY-LAND; PRYDZ-BAY; GARNET; LAMELLAE; PRESSURE; East Antarctica; Larsemann Hills; Prydz Bay; Antarc*; Antarctica; Enderby Land
• Online Access: https://hdl.handle.net/20.500.11897/400953; https://doi.org/10.1127/0935-1221/2003/0015-0055

Exsolution textures were observed in clinopyroxenes in mafic granulites from the Grove Mountains, East Antarctica. The first generation of exsolution occurs only in subcalcic augite megacrysts, in which coarse orthopyroxene lamellae exsolved parallel to the (100) plane. Electron microprobe reintegration of such augites yields a pre-metamorphic igneous temperature of ca. 970degreesC. The second generation of exsolution develops in both igneous and metamorphic clinopyroxenes. In metamorphic clinopyroxenes, two sets of very narrow pigeonite lamellae, subsequently inverted to orthopyroxene, exsolved parallel to (100) and (001) planes, respectively with 0degrees and 113degrees deviation to c-axis of the host. A peak metamorphic temperature of ca. 850degreesC was obtained from the reintegrated compositions of exsolved clinopyroxene, and an exsolution temperature of 740-770degreesC from the orientations of exsolved lamellae. The preservation of augite megacrysts and appearance of equilibrium assemblages suggests that mafic granulites from the Grove Mountains were formed during a single episode of high-grade metamorphism. Temperature estimates for original pyroxene crystallization and pigeonite exsolution from clinopyroxene host provide a good constraint on the peak conditions for this metamorphic event. In contrast with the Prydz Bay area, it is proposed that the Pan-African metamorphism in East Antarctica had reached a higher temperature of ca. 850degreesC, and later underwent a slow cooling process, which probably resulted from the magmatic underplating of the lower crust. Mineralogy SCI(E) 15 ARTICLE 1 55-65 15