Structural analyses of the crystalline rocks between Dirang and Tawang,West Kameng district,Arunachal Himalaya |
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| Authors: | Hari B Srivastava Vaibhava Srivastava Rajesh K Srivastava Chandra Kant Singh |
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| Institution: | (1) CNR, Istituto di Geoscienze e Georisorse, Sezione di Torino, Via Accademia delle Scienze 5, 10123 Torino, Italy;(2) Dipartimento di Scienze della Terra, Via Accademia delle Scienze 5, 10123 Torino, Italy |
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| Abstract: | In Kameng Valley of Arunachal Pradesh, the crystalline rocks of Se La Group of Higher Himalaya are thrust over the Lesser
Himalayan rocks of Dirang Formation, Bomdila Group along the Main Central Thrust and exhibit well preserved structures on
macro- to microscopic scales. Detailed analysis of structures reveals that the rocks of the area have suffered four phases
of deformation D1, D2, D3 and D4. These structures have been grouped into (i) early structures (ii) structures related to progressive ductile thrusting and
(iii) late structures. The early structures which developed before thrusting formed during D1 and D2 phases of deformation, synchronous to F1 and F2 phases of folding respectively. The structures related to progressive ductile shearing developed during D3 phase of deformation, when the emplacement of the crystalline rocks took place over the rocks of Dirang Formation along the
Main Central Thrust. Different asymmetric structures/kinematic indicators developed during this ductile/brittle-ductile regime
suggest top-to-SSW sense of movement of the crystalline rocks of the area. D4 is attributed to brittle deformation. Based on satellite data two new thrusts, i.e. Tawang and Se La thrusts have been identified
parallel to Main Central Thrust, which are suggestive of imbricate thrusting. Strain analysis from the quartz grains of the
gneissic rocks reveals constriction type of strain ellipsoid where k value is higher near the MCT, gradually decreases towards
the north. Further, the dynamic analysis carried out on the mesoscopic ductile and brittle-ductile shear zones suggest a NNE-SSW
horizontal compression corresponding to the direction of northward movement of Indian Plate. |
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