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P–T–t paths and post-metamorphic exhumation of the Day Nui Con Voi shear zone in Vietnam |
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| Authors: | Tran Ngoc Nam Mitsuhiro Toriumi and Tetsumaru Itaya |
| Institution: | aGeological Institute, University of Tokyo, 7-3-1 Hongo, Tokyo 113, Japan bResearch Institute of Natural Sciences, Okayama University of Science, 1-1 Ridai, Okayama 700, Japan |
| Abstract: | The Day Nui Con Voi belt in Vietnam is the southeasternmost part of the Red River shear zone in Asia. It is a narrow high-grade metamorphic core complex consisting of garnet–sillimanite–biotite gneisses, mylonite bands, amphibolite layers and migmatites. Geothermobarometric study of the complex revealed that the peak metamorphism took place under amphibolite-facies conditions of 690?60+30°C and 0.65±0.15 GPa and the subsequent mylonitization occurred under greenschist-facies conditions of  480°C and under 0.3 GPa. Fifteen synkinematic hornblende and biotite separates from gneisses, amphibolites and mylonites were dated with the K/Ar method. Hornblende separates from the Day Nui Con Voi give K–Ar ages of 26.4–28.5 Ma, and the biotite separates do give 24.5–24.7 Ma. Combination of thermobarometric and geochronological data yields the cooling history of 500°C at 28 Ma and 300°C at 24 Ma with a cooling rate of 70–110°C Ma?1, and 23 km post-metamorphic exhumation of the core complex. The first 16 km exhumation from the peak of metamorphism (at probably 31 Ma) to 28 Ma was triggered by the left-lateral strike-slip displacement of the Red River shear zone. |
| Keywords: | P–T–t paths K–Ar age exhumation cooling history Red River shear zone Vietnam |
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