Metamorphism and geochronology of the spinel−cordierite granulite in the Mirror Peninsula, East Antarctica

• Main Authors: LIU Xinshu, WANG Wei-(RZ), BAO Hong, GONG Tingnan, ZHAN Liqing, LIU Xiaochun, ZHAO Yue
• Format: Article in Journal/Newspaper
• Language: Chinese
• Published: Institute of Geomechanics, Chinese Academy of Geological Sciences 2023
• Subjects: east antarctica; spinel−cordierite granulite; p−t path; high−ultrahigh metamorphism; phase equilibrium modelling; Geology; QE1-996.5; Antarc*; Antarctica; East Antarctica; Prydz Bay
• Online Access: https://doi.org/10.12090/j.issn.1006-6616.2023172; https://doaj.org/article/e7dfc821e9a44182a8d1cb6fc6d26c55

Objective The Prydz Bay belt in East Antarctica recorded two significant tectono-thermal events, the Grenvillian event and the Pan-African event, which are considered to be closely related to the evolution of the Rodinia and Gondwana supercontinents. However, the geological history and the tectonic nature of the two events remain controversial. Methods Mineralogical and petrological analyses, phase equilibria modelling and zircon geochronology are combined to investigate the spinel−cordierite granulite from the Mirror Peninsula in order to better understand the tectono-thermal history of the Prydz Bay belt. Results The spinel−cordierite granulite contains different stages of mineral assemblages. The major stage of mineral assemblage involves cordierite, spinel, biotite, sillimanite, K-feldspar and minor garnet and ilmenite. The later stage of mineral assemblage is indicated by the emergence of magnetite as the increasing volumes of biotite and cordierite. Minor garnet and corundum are locally preserved, implying the mineral reaction ‘g+cor→sp+sill’ and more garnet and corundum in the peak stage. The garnet grains consist of 70%−72% almandine, 20%−22% pyrope, ~4% grossularite and ~4% spessartine. The XFe (Fe2+/(Fe2++Mg2+)) of representative garnet grains ranges from 0.77 to 0.80. The spinel exhibits an XFe range from 0.80 to 0.86. Different cordierite grains have similar compositions with Al of 3.89−3.93 a.p.f.u (atoms per formula unit) and XFe of 0.32−0.36. Biotite has high TiO2 (4.13%−5.23%) and Ti (0.23−0.30 a.p.f.u). K-feldspar grains consist of 78%−85% orthoclase, 15%−23% albite and ~1% anorthite. Based on the mineral compositions and phase equilibrium modelling, the pressure−temperature (P−T) conditions of the major stage of mineral assemblage are constrained to 870−910 °C and 0.64−0.69 GPa, followed by later retrogression to 810−820°C and 0.49−0.53 GPa. A peak stage with higher P−T conditions (T>910 ℃, P>0.69 GPa) can be inferred based on the relict peak minerals and characteristic mineral ...