Deformation and Melting, Reru Valley, High Himalayan Crystalline

Contents:

 

Deformation
a) Mylonites
b) Asymmetric shear zones
c) Constrictional deformation
d) Folding and transposition

 

Melting
e) Axial planar leucosomes
f) leucosomes on extensional shear zones
g) leucosomes on contractional shear zones
h) leucosomes cross-cutting foliation
i) melt interacting with folds

DEFORMATION IN RERU VALLEY. This valley runs N-S, from the Zanskar Shear Zone in the North close to the village of Reru, into the high grade, anatectic rocks of the High Himalaya Crystalline.

 

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a) Mylonites

 

Figure 1a)  Feldspar porphyritic mylonite with strongly folded Tml-leucogranite dyke. Sense of shear: sinistral as indicated by phenocryst asymmetry and C' foliation .	Figure 1b)  porphyroblastic mylonite, granitic protolith

 

Figure 2a)  Two sides of typical Ms-Bt mylonitic granite showing intense lineation.	Figure 2b)  Folded coarse gneiss

Figure 2d) Sillimanite-biotite schist with leucosome having diffuse boundaries suggesting in situ origin. Lack of spatial relationship with sillimanite suggest that melting is unrelated to the presence of sillimanite.	Figure 2e) Folded sillimanite-biotite schist intruded by tourmaline leucogranite with irregular boundaries and narrow melanosome rim in places. Rock face close to parallel with foliation. The leucogranite is unrelated to sillimanite grains (left of coin).	Figure 2f) Folded biotite-rich diatexite with refractory layers.

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b) Localized Shearing and Asymmetric Shear Zones

 

Figure 3a) Typical migmatite orthogneiss with voluminous leucosomes with equally spaced, localized shear bands, formed after anatexis.	Figure 3b) Similar to 3a but shear bands developed in the presence of melt which flowed through the shear plan.

Figure 3c) Asymmetric drag fold across shear zone. On the upper side the fold is wide, on the lower side it is sharp taking place over 1 cm.	Figure 3b)

 

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c) Constrictional Deformation

 

Figure 4a) Three sides of a feldspar porphyritic rock showing intense stretching of phenocrysts on two sides (left and top) and no significant deformation on the third side (right)	4b) Similar to (a)	4c) Two sides of a migmatitic block showing stretched leucosome on the left, in contrast to round leucosome cross section on the right.

 

Figure 4d) Migmatite with large proportion of leucosomes showing irregular foliation (perhaps radial) interpreted to represent constriction and stretching perpendicular to the plane	4e) Another example from the same block as (d).

 

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d) Folding and transposition

 

Figure 5a) unfinished.	Figure 5b) unfinished.	Figure 5c) unfinished.

 

Figure 5d and e) unfinished	Figure 5e) Same as d but a later stage of evolution of a melt-lubricated fold-thrust.	Figure 5f) unfinished.

 

 

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