Zanskar Shear Zone

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


a) The "main shear plane" at Reru defining typical topography.	b) Leucogranite sills accumulated underneath the plane on(a).

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).

e) The shear zone to the west of Pensi La (no further information available).	f) Same.

Granite accumulation at high strain zone


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).

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).

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.

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.


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.

c) Same as (b) (ZNK09-23 N33 14' 19.0" E 77 05'58.2").	d) Same as (b).

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).

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.