K-Ar Dating of Fault Gouges from the Red River Fault Zone of Vietnam

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• 作者：Hoang Bac BUI ; Xuan Thanh NGO ; Yungoo SONG ; Tetsumaru ITAYA ; Koshi YAGI ; The Hung KHUONG and Tien Dung NGUYEN
• 刊名：Acta Geologica Sinica - English Edition
• 出版年：2016
• 出版时间：October 2016
• 年：2016
• 卷：90
• 期：5
• 页码：1653-1663
• 全文大小：10780K
• ISSN：1755-6724

文摘

Constraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes. This paper presents the first authigenic illite K-Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province, Vietnam. The fault gouge samples were separated into three grain-size fractions (<0.1 µm, 0.1–0.4 µm and 0.4–1.0 µm). The results show that the K-Ar age values decrease from coarser to finer grain fractions (24.1 to 19.2 Ma), suggesting enrichment in finer fraction of more-recently grown authigenic illites. The timing of the fault movement are the lower intercept ages at 0% detrital illite (19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma). In combination with previous geochronological data, this result indicates that the metamorphism of the Day Nui Con Voi (DNCV) metamorphic complex took place before ca. 26.8 Ma. At about 26.8 Ma-25 Ma, the fault strongly acted to cause the rapid exhumation of the rocks along the Red River-Ailoa Shan Fault Zone (RR-ASFZ). During brittle deformation, the DNCV slowly uplifted, implying weak movement of the fault. This brittle deformation might have lasted for ca. 5 Ma.