Granulite facies paragneisses from the middle segment of the Mogok metamorphic belt, central Myanmar

Thu, Ye Kyaw; Enami, Masaki; Kato, Takenori; Tsuboi, Motohiro

doi:10.2465/jmps.160526

Cited by 15 publications

(13 citation statements)

References 42 publications

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“…The chemical formulae of minerals employed for reactions discussed on the following pages are after Holland and Powell (). The pressure at peak granulite facies stage was assumed to be 0.8 GPa, considering equilibrium conditions estimated for the paragneiss surrounding the marble and calcsilicate rock (Ye Kyaw Thu et al., , ).…”

Section: Discussionmentioning

confidence: 99%

“…Figure summarizes the P–T conditions of the peak granulite facies and subsequent low‐amphibolite facies stage, and compares the compositions of metamorphic fluids of the marble and the calcsilicate rock of the Mogok metamorphic belt between the two stages of recrystallizations. Low

X_{{normalCO}_{2}}

fluid composition of paragneiss surrounding the metacarbonate rocks, which is inferred based on their carbonate minerals‐absent assemblages (Maw Maw Win et al., ; Ye Kyaw Thu et al., , ), was also shown for comparison.…”

Section: Discussionmentioning

confidence: 99%

“…These areas are denoted as the Onzon–Thabeikkyin region, hereafter, unless otherwise noted. Paragneiss, marble and calcsilicate rock occupy the middle segment of the Mogok metamorphic belt from Mandalay to Mogok regions (Maw Maw Win, Enami, Kato, & Ye Kyaw Thu, ; Maw Maw Win et al., ; Ye Kyaw Thu, Enami, Kato, & Tsuboi, ; Ye Kyaw Thu, Maw Maw Win, Enami, & Tsuboi, ; Yonemura et al., ), continuing southwards, where they become less dominant. The metamorphic lithologies in this region form a zone with an average width of 40 km and consist of various types of marble and calcsilicate rock with paragneiss of granulite facies.…”

Section: Geological Settingmentioning

confidence: 99%

“…Biotite coexisting with rutile and/or ilmenite has high TiO 2 , of up to 6.9 wt% (Ye Kyaw Thu et al., ). Conventional geothermobarometers and Zr‐in‐rutile geothermometers yield P–T conditions of 0.60–0.84 GPa/780–860°C as the peak granulite facies metamorphism (Ye Kyaw Thu et al., , ). These paragneiss were extensively recrystallized under lower amphibolite facies conditions (~0.40–0.55 GPa/620–640°C) during the exhumation and hydration stage.…”

Section: Geological Settingmentioning

confidence: 99%

“…Ye Kyaw Thu et al. (, ) estimated the equilibrium temperatures of paragneiss from the Onzon and Thabeikkyin areas as 780–860°C at 0.60–0.84 GPa based on conventional geothermobarometers employing partial assemblages of Grt+Bt+Pl+Crd+Spl+Sill+Qz and empirical Ti‐in‐biotite and Zr‐in‐rutile geothermometers. Yonemura et al.…”

Section: Calcite–dolomite Solvus Geothermometermentioning

confidence: 99%

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Evolution of metamorphic fluid recorded in granulite facies metacarbonate rocks from the middle segment of the Mogok metamorphic belt in central Myanmar

Thu

Enami

2018

Journal Metamorphic Geology

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The Mogok metamorphic belt of Palaeogene age, which records subduction‐ and collision‐related events between the Indian and Eurasian plates, lies along the western margin of the Shan plateau in central Myanmar and continues northwards to the eastern Himalayan syntaxis. Reaction textures of clinohumite‐ and scapolite‐bearing assemblages in Mogok granulite facies metacarbonate rocks provide insights into the drastic change in fluid composition during exhumation of the collision zone. Characteristic high‐grade assemblages of marble and calcsilicate rock are clinohumite+forsterite+spinel+phlogopite+pargasite/edenite+calcite+dolomite, and scapolite+diopside+anorthite+quartz+calcite respectively. Calculated petrogenetic grids in CaO–MgO–Al2O3–SiO2–H2O–CO2 and subsets of this system were employed to deduce the pressure–temperature–fluid evolution of the clinohumite‐ and scapolite‐bearing assemblages. These assemblages suggest higher temperature (>780–810°C) and XnormalCO2 [=CO2/(CO2+H2O) >0.17–0.60] values in the metamorphic fluid for the peak granulite facies stage, assuming a pressure of 0.8 GPa. Calcite grains commonly show exsolution textures with dolomite particles, and their reintegrated compositions yield temperatures of 720–880°C. Retrograde reactions are mainly characterized by a reaction zone consisting of a dolomite layer and a symplectitic aggregate of tremolite and dolomite grown between clinohumite and calcite in marble, and a replacement texture of scapolite by clinozoisite in calcsilicate rock. These textures indicate that the retrograde reactions developed under lower temperature (<620°C) and XnormalCO2 (<0.08–0.16) conditions, assuming a pressure of 0.5 GPa. The metacarbonate rocks share metamorphic temperatures similar to the Mogok paragneiss at the peak granulite facies stage. The XnormalCO2 values of the metacarbonate rock at peak metamorphic stage are, however, distinctly higher than those previously deduced from carbonate mineral‐free paragneiss. Primary clinohumite, phlogopite and pargasite/edenite in marble have F‐rich compositions, and scapolite in calcsilicate rock contains Cl, suggesting a contrast in the halogen compositions of the metamorphic fluids between these two lithologies. The metamorphic fluid compositions were probably buffered within each lithology, and the effective migration of metamorphic fluid, which would have extensively changed the fluid compositions, did not occur during the prograde granulite facies stage throughout the Mogok metamorphic belt. The lower XnormalCO2 conditions of the Mogok metacarbonate rocks during the retrograde stage distinctly contrast with higher XnormalCO2 conditions recorded in metacarbonate rocks from other metamorphic belts of granulite facies. The characteristic low XnormalCO2 conditions were probably due to far‐ranging infiltration of H2O‐dominant fluid throughout the middle segment of the Mogok metamorphic belt under low‐amphibolite facies conditions during the exhumation and hydration stage.

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Section: Discussionmentioning

confidence: 99%