40Ar/39Ar geochronology constraints on the formation age of Myanmar jadeitite

The jadeitite that occurs in Myanmar is one of the largest and most important jadeite deposits in the world. However, the formation age of the Myanmar jadeitite remains poorly constrained. Here, we conduct an integrated study using petrology and 40Ar/39Ar geochronology to analyze the Myanmar jadeitite. Petrological observations show that the studied jadeitite consists mainly of jadeite minor sodic-calcic amphibole and analcime and that the jadeitite was cut by late amphibole rock consisting of sodic amphibole and minor chlorite. 40Ar/39Ar laser stepwise heating dating of jadeite from the jadeitite yielded a plateau age of 123.9 +/- 3.4 Ma, the sodic-calcic amphibole associated with jadeite yielded a plateau age of 134.8 +/- 1.4 Ma, and the sodic amphibole of late amphibole rock yielded a plateau age of 92.7 +/- 1.2 Ma. These results indicate that the studied jadeitite was formed during the early Cretaceous from (135 Ma) high-pressure (HP) metasomatism and then experienced a late Cretaceous (93 Ma) HP metasomatism. Combining our results with previous studies using petrography and geochronology, we suggest that the formation process of Myanmar jadeitite involved multistages of metasomatism. (C) 2013 Elsevier B.V. All rights reserved.