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Journal of the Geological Society

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Ion microprobe zircon U–Pb age and geochemistry of the Myanmar jadeitite

¹ China University of Geosciences, Beijing 100083, China (e-mail: shiguanghai{at}263.net.cn)
² Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³ School of Earth and Space Sciences, Peking University, Beijing 100871, China
⁴ Guangdong Province Material Testing Center, Guangzhou 510080, China
⁵ SHRIMP Laboratory, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China

Combined geochemistry and geochronology of the Myanmar jadeitite were determined. Bulk-rock trace element compositions display U-shaped REE patterns with pronounced positive Eu anomalies. The total REE abundances are very low, less than half chondritic, and the high field strength elements and some large ion lithophile elements are moderately enriched. These features indicate a metasomatic origin. There are three groups of zircons with different interior characteristics, cathodoluminescence, mineral inclusions, chemical compositions and sensitive high-resolution ion microprobe U–Pb ages. Group-I zircons, with a mean age of 163.2 ± 3.3 Ma, mostly have distinct oscillatory zoning, highest U and Th contents, and Na-free, Mg-rich mineral inclusions, and thus indicate an igneous (formation of oceanic crust) or hydrothermal (serpentinization and/or rodingitization) event in the Middle Jurassic. Group-II zircons, with a mean age of 146.5 ± 3.4 Ma, have bright luminescence without oscillatory zoning and include jadeite and jadeitic pyroxene inclusions, suggesting that formation of the Myanmar jadeitites, as well as subduction of the eastern Indian oceanic plate, occurred in the Late Jurassic. Group-III zircons have an age of 122.2 ± 4.8 Ma, which represents a later unknown thermal event. Discovery of the Middle Jurassic zircons provides geochronological constraint on the tectonic evolution of the eastern Indo-Burman Range.