Abstract
In Gonto La valley, southern Tibet, a continuous, planar,
~10°N dipping detachment horizon juxtaposes Tethyan slates
over a footwall of leucogranite that intrudes a S-dipping
injection complex layer that I regard as a rotated Southern Tibet
Detachment System (STDS) horizon. This is deformed & partially
cut by the leucogranite which forms a pluton extending throughout
Khula Kangri massif. In collaboration, 208Pb-232Th measurements on
12 monazite grains of the leucogranite gave a crystallization age
of 12.5 ± 0.4 Ma. Integrated estimates of magnitude, and
rate, of detachment displacement suggest that STDS displacement
continued after granite crystallisation for 1-3 m.y. Therefore N-S
extension in southern Tibet continued into the Late Miocene. A new
geologic map of the Khula Kangri and Kanga Punzum-Monlakarchung
High Nimalayan ranges is presented using field, satellite &
topographic data. These define a fork in the High Himalaya that
results in a repetition of the main geological section. The STDS
can be traced around both ranges and is a continuous surface. A
simple model of post detachment, scissor faulting and block
rotation is proposed. In SE Nanga Parbat Haramosh Massif (NPHM),
Pakistan, field and microstructural analysis of strain and sense
of shear trends indicate that several km of metasedimentary
schists and gneisses are Himalayan Main Mantle Thrust (MMT)
footwall rocks rotated to vertical due to NW-SE directed
shortening. Near the NPHM summit region, several km of
non-coaxially sheared granitic orthogneiss show W over E
displacement structures. Although deformation mechanisms appear
lower temperature than in the MMT footwall rocks, a major "uplift"
structure (the Rupal Chichi shear zone - RCSZ) is proposed. To the
SW, an E-over W shear zone (the Diamir Shear Zone - DSZ) that
coincides with a syn-kinematically intruded granite (the Jalhari
Granite) is recognised. In collaboration, 208Pb-232 Th
measurements on monazite grains of the Jalhari indicate
displacement has continued from ~9 to <3 Ma. The DSZ is
regarded as the mechanical continuation of the Raikot Fault. The
Raikot-DSZ, together with the RCSZ define a conjugate pair that is
interpreted to mark a pop-up structure, allowing the skywards
displacement of NPHM.
Edwards, M.A., 1998. Examples of tectonic mechanisms for local
contraction and exhumation of the leading edge of India. Southern
Tibet (28-29N; 89-91E) and Nanga Parbat, Pakistan. Unpublished PhD
dissertation, State University of New York at Albany. 315pp., +xi;
2 folded plates (maps)
University at Albany Science Library call number: SCIENCE
MIC Film QC 869 Z899 1998 E393
Copies of this PhD dissertation can be ordered
from Proquest UMI
Front matter (title,
table of contents, abstract, acknowledgements) - 0.4MB pdf
file
Photo pages in dissertation
(colour
and greyscale photos and figures with captions): - 36.6MB
pdf file
Plate 1 - Geologic
map
of Yamdrok portion of INDEPTH II seismic traverse
(coloured geological map; scale
~1:143,500)
Appendix A - Geological
summary of Plate 1 - 0.1MB pdf file
Plate 2 - Geologic
map
of
outcrops in southern Nanga Parbat - Haramosh massif
(coloured outcrop geological map; scale
1:75,000)
Data tables and lists;
sample locations:
Table 5.1 - Recognised
senses of shear from locations in SE NPHM & Dichil/E. Astor
- 0.7MB pdf file
Tables 5.2-5.5 - Sample
and thin section listings; abbreviation explanation - 0.9MB
pdf file
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