Constraints on the stratigraphic age of metasedimentary rocks from the Larsemann Hills, East Antarctica: possible implications for Neoproterozoic tectonics
1995; Elsevier BV; Volume: 75; Issue: 3-4 Linguagem: Inglês
10.1016/0301-9268(95)80005-3
ISSN1872-7433
AutoresYue Zhao, Xiaohan Liu, Biao Song, Zongqing Zhang, Jiliang Li, Yupeng Yao, Yanbing Wang,
Tópico(s)Geochemistry and Geologic Mapping
ResumoIn this study we investigate crystallization ages of detrital zircon from paragneiss from the Larsemann Hills, East Antarctica, using the single zircon PbPb thermal evaporation technique. The 207Pb/206Pb ages of eleven detrital zircons range from 1200 ± 6(σ) Ma to 766 ± 12(σ) Ma. Although these ages must be regarded as minimum crystallization ages, investigation of the U content and damage state of the internal crystal structure using fission track analysis suggests that they may approach crystallization ages. This is confirmed by zircons from a granitic orthogneiss (W20401), which show consistent radiogenic Pb ratios released during the final evaporation steps. The 207Pb/206Pb age of this orthogneiss is 940 ± 6(σ) Ma, similar to its whole-rock RbSr isochron age of 1024 ± 45(σ) Ma (IR = 0.7241 ± 40). Its SmNd model age (TDM) is about 2.2 Ga. Further Sm Nd model ages (TDM) include 2.1 Ga for the paragneiss, and 1.6–1.7 Ga for a 0.55 Ga granite. The presented field and isotopic chronological data suggest that: (1) the 1-Ga event represents emplacement of the orthogneiss protolith, but does not necessarily involve high-grade metamorphism; (2) deposition of the paragneiss protoliths occurred during the Neoproterozoic, which suggests that accretion of the East Antarctic craton had not been completed until the early Palaeozoic; (3) deformation and granulite facies metamorphism in the region can be attributed to the ∼ 0.5-Ga ('Pan-African') event.
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