Pressure-temperature-time path discontinuity in the Main Central Thrust zone, central Nepal

Metapelites collected in central Nepal reveal a discontinuity in metamorphic pressure- temperature-time (P-T-t) paths near the base of the Main Central thrust zone, despite an absence of obvious structural breaks. Garnets in the structurally lowest rocks grew with increasing T and P (loading), where...

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Bibliographic Details
Published in:Geology (Boulder) 2001-07, Vol.29 (7), p.571-574
Main Authors: Kohn, Matthew J, Catlos, Elizabeth J, Ryerson, Frederick J, Harrison, T. Mark
Format: Article
Language:English
Subjects:
absolute age
Asia
Cenozoic
central Nepal
Darondi River valley
dates
faults
garnet group
geologic barometry
geologic thermometry
Geological time
Geology
igneous and metamorphic rocks
Indian Peninsula
Indian Plate
ion probe data
Main Central Thrust
mass spectra
metamorphic rocks
metamorphism
metapelite
metasedimentary rocks
Miocene
monazite
Neogene
Nepal
nesosilicates
orthosilicates
P-T conditions
P-T-t paths
Pb/Th
Petrology
phosphates
plate tectonics
Pressure
reactivation
relaxation
silicates
spectra
Structural geology
Temperature
Tertiary
thrust faults
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Summary:Metapelites collected in central Nepal reveal a discontinuity in metamorphic pressure- temperature-time (P-T-t) paths near the base of the Main Central thrust zone, despite an absence of obvious structural breaks. Garnets in the structurally lowest rocks grew with increasing T and P (loading), whereas garnets 1-3 km upsection grew with increasing T, but decreasing P (exhumation). Monazite grains in structurally lower rocks yield ion- microprobe Th-Pb ages of 8-9 Ma. Structurally higher monazite grains range from 10 to 22 Ma. The P-T-t paths confirm previous interpretations that footwall metamorphism in part resulted from thrust reactivation ca. 8 Ma, but also reflect thermal relaxation following older (20 Ma or older) thrust movement. The Main Central thrust zone formed during pulses of movement that resulted in progressive transfer of material from the lower to upper plate.
ISSN:0091-7613
1943-2682
DOI:10.1130/0091-7613(2001)029<0571:PTTPDI>2.0.CO;2