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Late Eocene-Oligocene granulite facies garnet-sillimanite migmatites from the Mogok Metamorphic belt, Myanmar, and implications for timing of slip along the Sagaing Fault

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Date
04/2021
Author
Lamont, T.N.
Searle, M.P.
Hacker, B.R.
Htun, K.
Htun, K.M.
Morley, C.K.
Waters, D.J.
White, R.W.
Keywords
Granulite facies migmatites
Biotite dehydration melting
Petrological modelling
U–Pb monazite geochronology
Mogok Metamorphic belt
Sagaing Fault
GE Environmental Sciences
DAS
AC
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Abstract
The Mogok Metamorphic Belt (MMB) in Myanmar is a polymetamorphic, mainly Paleogene granulite-uppermost amphibolite facies terrane consisting mainly of marbles and calc-silicates hosting spinel, ruby and sapphire. Jurassic charnockite-syenite intrusions, as well as Eocene-Miocene leucogranite intrusions are also present. Pelitic rocks are uncommon, and where present, have sillimanite, both as primary inclusions in garnet and as secondary Bt + Sil coronas around garnet. Core samples from the Kyi-Tauk-Pauk gold mine at Thabeikkiyin, north of Mandalay, are mostly Grt + Bt + Sill gneisses and migmatites with uncommon interbanded Opx + Grt + Bt gneisses. Pseudosection modelling suggests prograde garnet growth occurred by biotite-dehydration melting that reached peak P–T conditions of 870–970 °C and ~ 0.9 GPa, and was followed by garnet breakdown forming coarse retrograde Bt + Sil coronas. U[sbnd]Pb monazite data show an early high-grade granulite event at 43–32 Ma, and a later upper amphibolite sillimanite-grade event peaking at 23–20 Ma, with a change in monazite chemistry after c. 22 Ma that is consistent with fluid/(melt) interaction and garnet breakdown. Elevated Th/U ratios from ~35 to 22 Ma, and at ~18 Ma are compatible with melt influx at that time, timing that is similar to the age of the regional Kabaing leucogranite in the Mogok valley area. Our data show that peak granulite facies metamorphism along the Mogok Metamorphic belt was mainly Middle Eocene-Early Oligocene, with upper amphibolite facies metamorphism extending to earliest Miocene. The MMB is cut abruptly by the Sagaing fault, a large-scale dextral fault that extends from the Andaman Sea north to the East Himalayan syntaxis. Our new U[sbnd]Pb monazite data constrain the oldest age of initiation of the eastern branch of the cross-cutting Sagaing dextral strike-slip fault at
Citation
Lamont , T N , Searle , M P , Hacker , B R , Htun , K , Htun , K M , Morley , C K , Waters , D J & White , R W 2021 , ' Late Eocene-Oligocene granulite facies garnet-sillimanite migmatites from the Mogok Metamorphic belt, Myanmar, and implications for timing of slip along the Sagaing Fault ' , Lithos , vol. 386-387 , 106027 . https://doi.org/10.1016/j.lithos.2021.106027
Publication
Lithos
Status
Peer reviewed
DOI
https://doi.org/10.1016/j.lithos.2021.106027
ISSN
0024-4937
Type
Journal article
Rights
Copyright © 2021 Elsevier B.V. All rights reserved. This work has been made available online in accordance with publisher policies or with permission. Permission for further reuse of this content should be sought from the publisher or the rights holder. This is the author created accepted manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.lithos.2021.106027
Description
MPS is grateful to the Oxford-Burma Aung San Suu Kyi trust for funding research and field visits to Mogok. U-Th-Pb geochronology was funded by UCSB and NSF grants EAR-1348003 and EAR-1551054 to BH.
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URL
https://www.sciencedirect.com/science/article/pii/S0024493721000633?via%3Dihub#s0085
URI
http://hdl.handle.net/10023/24809

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