Metamorphic conditions and CHIME monazite ages of Late Eocene to Late Oligocene high-temperature Mogok metamorphic rocks in central Myanmar. (1st March 2016) - Maw Maw Win,
Highlights: We report petrological and mineralogical characteristics of high T / P type pelitic gneisses of Mogok metamorphic belt, Myanmar. We estimate metamorphic P – T conditions of pelitic gneisses. We declare CHIME monazite ages of Late Eocene–Oligocene on the Mogok metamorphic rocks, and compare them with published data. We discuss P – T – t history of the Mogok metamorphic belt. Abstract: The high temperature ( T )/pressure ( P ) regional Mogok metamorphic belt is situated in central Myanmar, and is mainly composed of pelitic gneisses, amphibolites, marbles, and calc-silicate rocks. The garnet–biotite–plagioclase–sillimanite–quartz assemblage and its partial system suggest equilibrium P / T conditions of 0.6–1.0 GPa/780–850 °C for the peak metamorphic stage, and 0.3–0.5 GPa/600–680 °C for the exhumation and hydration stage. Monazite grains show complex compositional zoning consisting of three segments—I, II, and III. Taking into consideration the monazite zoning and relative misfit curves, the calculated chemical Th–U–total Pb isochron method (CHIME) monazite age data (284 spot analyses) indicated four age components: 49.3 ± 2.6–49.9 ± 7.9, 37.8 ± 1.0–38.1 ± 1.7, 28.0 ± 0.8–28.8 ± 1.6, and 23.7 ± 1.3 Ma (2 σ level). The ages of the Late Eocene and Late Oligocene epochs were interpreted as the peak metamorphic stage of upper-amphibolite and/or granulite facies and the postdated hydration stage, respectively.