Kinematics of the Greater Himalayan sequence, Dhaulagiri Himal ...

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S =
1 2 1W 2
m
( ) 1 2
R XZ
+ R XZ
( )
( )
1 + 2 1+ W 2
m
2
1W m
1
2
( ) 1 2
+ R XZ
+ R 1 XZ
2
1
(2)
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where S, shortening perpendicular to the flow plane; S -1 , stretch parallel to flow plane (for plane
strain at constant volume)
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Data from sample 070B yield shortening values perpendicular to the flow plane between
25-32%. Furthermore, assuming plane strain deformation, an assumption that is supported by
the cross-girdled quartz c-axis fabric for sample 070B and most other samples analyzed (Figure
8), stretch parallel to the flow plane is estimated at between 34-47% parallel to the flow plane.
As the neutral vorticity numbers estimated in this study are dependent on the last increment of
strain due to dynamic recrystallization (as values were determined from quartz c-axis
orientation data) it is likely that the above values underestimate the total stretch and shortening.
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All samples used to estimate vorticity, which were collected ~2 to 6 km above the MCT,
are within error of each other and indicate a significant component of pure shear deformation
(Figure 12). The average vorticity value estimated in this study is 0.67, which implies a pure
shear contribution of 53% and a simple shear contribution of 47% in the lower portion of the
Greater Himalayan sequence exposed in central Nepal.
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6. Discussion
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6.1 Position of the Main Central thrust
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Detailed geological mapping and microstructral analyses provide evidence of pervasive
top-to-the-south ductile shearing at temperatures of ~500˚C through a crustal section that extends
for more than 8 km below the previously mapped position of the MCT in the Kali Gandaki
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