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Zanskar Shear Zone, NW India


Gumbaranjon injection network

Roberto Weinberg and Pavlina Hasalova
Monash University, Australia



Copyright 2004-2011 by Roberto Weinberg. All rights reserved. Unlimited permission to copy or use is hereby granted for non-profit driven enterprise, subject to inclusion of this copyright notice and acknowledgment of the source URL:


I would very much appreciate an email stating how this material will be used: Roberto Weinberg, Monash University, Australia. Thanks, RW.


DISCLAIMER. The material on this website has not undergone the scrutiny of Monash University and does not conform to its corporate web design. It is entirely based on a free-spritied, curiosity-driven research effort by the author, and therefore in no way expresses the official position of the University.



Zanskar Shear Zone: four main characteristics
a) normal shearing overprinting an older thrusting event,
b) trends roughly E-W, from Gumbaranjon in the east, where it curves to a N-S orientation, to Pensi La in the west and beyond,
c) Shear is maximum close to a lithological contact between a metasedimentary sequence characterized by Bt-quartzites and schists and high-grade orthogneiss/migmatite terrane. This contact is also a steep gradient in metamorphic grade,
d) both trhusting and normal shearing are contemporaneous with leucogranite magmatism, as inferred from variety of strain in dykes e) leucogranite derived from footwall migmatites accumulates close to this contact.


subsections below:
High strain zone: characteristic morphology
Granite accumulation at contact/high strain zone
Early Thrusting
Normal movement overprinting thrusting
Timing in relation to leucogranites


Characteristic morphology of high strain zone: from Reru to Pensi La




Zanskar shear plane Zanskar shear plane
a) The "main shear plane" at Reru defining typical topography. b) Leucogranite sills accumulated underneath the plane on(a).
Zanskar shear plane Zanskar shear plane
c) The "main shear plane" at Mune Gompa. d) The "main shear plane" at Pensi La separating a lighter rock mass (presumably orthogneisses and granites) below from a metasedimentary rocks (presumably biotite quartzites and schists).
Zanskar shear plane Zanskar shear plane
e) The shear zone to the west of Pensi La (no further information available). f) Same.



Granite accumulation at high strain zone


leucogranite injection leucogranite injection
a) Injection complex below the Gumbaranjon peak. This complex is characterized mostly by layer parallel sills of Tml-Gnt-Ms-Bt leucogranite. b) detail of (a).
leucogranite injection leucogranite injection
c) Gumbaranjon peak showing leucogranite intrusions, mostly sills parallel to the main shear foliation, cut by a steep (60 degree) normal fault. Granite intrusions decrease upwards into a dominantly biotite quartzite and biotite (garnet-staurolite) schist. d) detail of (a).
leucogranite injection leucogranite injection
e) Leucogranite injection complex, Gumbaranjon area. f) Same but further up the mountain side. The patch of snow in the middle matches the one in (e). Notice decrease in density of intrusion.
leucogranite injection
g) Leucogranite injection complex, Tangsyo-Key valley. Granite sheets have different angles in relation to the dominant, gently dipping to the north (right) bedding/shear plane. The marked layer of country rock has granite sheets at high angle to the shear plane, whereas above this layer granite sheets are sheared towards the dominant thrust plane, and seem to define the characterising stepping upwards to the right indicative of high strain in a top-to-the-north normal shear zone. Scale: estimated 200-300m in vertical. h) ????


Early thrusting


From Pune towards Mune, layered biotite schists and biotite psammites/quartzites define a thrust that is overprinted by normal shearing. Thrusting is associated with large scale inclined to recumbent folds (see (g) and (h)) verging S to E. The thrust package is at least 1km thick across strike (to be measured). At a small scale the rocks have a well-defined asymmetric crenulation with vergence to the S to SE to E. more exactly.



leucogranite injection leucogranite injection
a) Thrusting to the SE on the north side of Kargyak Chu (ZNK09-23 N33 14' 19.0" E 77 05'58.2"). Notice bending of steep foliation planes into gently dipping planes. Scale ~50-100 m in vertical. b) Thrusts at a smaller scale striking at N10E/25E, lcren=352/0-5 (motion interpreted to be perpendicular to crenulation, to the E, based on stretching lineation in other neighbouring outcrops.
leucogranite injection leucogranite injection
c) Same as (b) (ZNK09-23 N33 14' 19.0" E 77 05'58.2"). d) Same as (b).
leucogranite injection leucogranite injection
e) Thrust plane striking N58E/35SE Lint= 057/00, S-C fabric and drag folds perpendicular to Lint indicate thrusting to the NW. The sheared rock is an orthogneiss with leucosomes, and tml-leucogranite is discordant (post-dates thrusting (ZNK09-31 N33 18' 23.1" E 76 58'52.1"). f) Detail of (e).
leucogranite injection leucogranite injection
g) Thrust plane dipping gently to the right and steeper bedding defining sense of movement to the left on photograph (ZNK09-24 N33 14' 22.3" E 77 09'59.3"). Scale estimated at ~50 m in vertical. h) Large scale recumbent to inclined asymmetric folds verging to the E and riding on thick thrust planes. Notice the river at the bottom right hand-side. Scale estimated at ~50 m in vertical.


Zanskar Shear Zone: Normal movement overprinting thusting



The early thrusting phase is overprinted by the normal movement that defines the Zanskar Shear Zone. There are a number of wide normal shear zones, which increases in width towards a regional lithological contact between the Bt-schists / Bt-psammites-quartzites and orthogneisses. Normal movement is presumably responsible for a steep metamorphic gradient iand seems to have explored thislithological contact An excellent new road cut exposes the main shear zone at this contact approaching Reru from the east, where the early event has been erased. The overprinting relationships are to be found in transitional zones.


normal shear zone normal shear zone
a) Normal pervasive shearing on gentle plane (shear sense to the right). Scale: tens of metres in horizontal. Close to Reru. b) Normal pervasive shearing on gentle plane (shear sense to the right) PROVIDE LOCATION AND ATTITUDE. Scale: tens of metres in horizontal.Close to Reru.
normal shear zone normal shear zone
c) Steep normal shear band 50 cm- 1 m wide. d) Normal shearing of heterogeneous orthogneiss. Close to Reru. THIS SECTION IS MISSING THE OVERPRINT RELATIONSHIP