Excess argon in phengite from eclogite: Evidence from dating of eclogite minerals by SmNd, RbSr and 40Ar39Ar methods
1994; Elsevier BV; Volume: 112; Issue: 3-4 Linguagem: Inglês
10.1016/0009-2541(94)90033-7
ISSN1872-6836
AutoresShuguang Li, Songshan Wang, Chen Yizhi, Deliang Liu, Ji Qiu, Zhou Hong-xing, Zhimin Zhang,
Tópico(s)earthquake and tectonic studies
ResumoThe existence of excess Ar in phengites from coesite-bearing ultrahigh-pressure eclogites of the Dabie Mountains and SuLu terrain, China, has been confirmed by dating of minerals using SmNd, RbSr and 40Ar39Ar methods. 40Ar39Ar ages of phengites for two samples studied are much older than the SmNd and RbSr mineral isochron ages: sample QL-1 has RbSr age of 219.5 ± 0.5 Ma, SmNd age of 226.3 ± 4.5 Ma and phengite 40Ar39Ar age of 877.5 ± 15.9 Ma; the corresponding ages for sample Zb-4 are: 223.9 ± 0.9 Ma (RbSr), 228.4 ± 6.0 Ma (SmNd) and 943.3 ± 12.4 Ma (40Ar39Ar, phengite). An age of ∼225 Ma based on the SmNd and RbSr mineral isochron ages is consistent with the time inferred from paleomagnetic and geological data for collision of the North China and Yangtse Blocks and formation of these eclogites. We call for greater caution in 40Ar39Ar dating of phengites from other occurrences of ultrahigh-pressure environments.
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