地质力学学报2024，Vol.30Issue(3)：487-505,19.DOI:10.12090/j.issn.1006-6616.2023172
东南极米洛半岛尖晶石-堇青石麻粒岩变质作用与年代学研究
Metamorphism and geochronology of the spinel-cordierite granulite in the Mirror Peninsula,East Antarctica
摘要
Abstract
[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℃ and 0.64-0.69 GPa,followed by later retrogression to 810-820℃ 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 compositions(e.g.Ti in biotite).Zircon grains commonly show core-mantle-rim structures in cathodoluminescence(CL)images.The LA-ICP-MS zircon U-Pb dating analyses reveal a wide age range from 613±7 Ma to 877±9 Ma(except a maximum of 916±11 Ma)for the cores.The zircon bright rims yield a weighted mean age of 526±8 Ma with a wide range of Th/U(0.06-1.23),mostly higher than 0.1.[Conclusion]Based on the results,a few conclusions can be drawn:(1)The spinel-cordierite granulite recorded medium-low pressure/high-ultrahigh temperature metamorphism with a clockwise P-T evolution path and high dT/dP.(2)The results of zircon geochronological analysis show that zircon cores mainly record U-Pb ages in the range of 800～600 Ma,younger than typical ages of Grenvillian events,which may reflect younger inherited zircon cores or significant isotopic resetting.(3)The age of～530 Ma of zircon rims is interpreted to represent the post-peak cooling stage of the Pan-African tectono-thermal event.[Significance]This study examined the P-T conditions and the zircon ages of the spinel-cordierite granulite in the Mirror Peninsula.In combination with previous results,the P-T-t path constructed for the spinel-cordierite granulite provides new constraints on the evolution of the Prydz Bay belt during the Pan-African period.关键词
东南极/尖晶石-堇青石麻粒岩/P-T轨迹/高温—超高温变质/相平衡模拟Key words
East Antarctica/spinel-cordierite granulite/P-T path/high-ultrahigh metamorphism/phase equilibrium modelling分类
天文与地球科学引用本文复制引用
刘昕淑,王伟,保红,龚庭楠,湛礼卿,刘晓春,赵越..东南极米洛半岛尖晶石-堇青石麻粒岩变质作用与年代学研究[J].地质力学学报,2024,30(3):487-505,19.基金项目
国家自然科学基金项目(42172068,41941004,41530209,41672062) （42172068,41941004,41530209,41672062）
中国地质科学院基本科研业务费项目(JYYWF201819) （JYYWF201819）
中国地质调查局地质调查项目(DD20221810)This research is financially supported by the National Natural Science Foundation of China(Grants No.42172068,41941004,41530209,and 41672062),the Fundamental Research Funds of the Chinese Academy of Geological Sciences(Grant No.JYYWF201819),and the Geological Survey Project of the China Geological Survey(Grant No.DD20221810). （DD20221810）
