Kinematic Vorticity Analysis along the Karakoram Shear Zone, Pangong Mountains, Karakoram: Implications for the India–Asia Tectonics

Abstract

The Karakoram Shear Zone (KSZ) is a northwest-southeast trending dextral ductile shear zone that has mylonitized the Tangste and Darbuk granitoids of the southern margin of the Asian plate. Kinematic vorticity (W k ) has been estimated in 6 mylonitized Tangste granite samples, using Porphyroclast Hyperbolic Distribution (PHD) and Shear Band (SB) Analyses methods on well-developed quartz and feldspar porphyroclasts, and synthetic and antithetic shear bands respectively to visualize the overall deformation of the KSZ. The PHD and SB analyses yield W k values ranging from W k =0.29 to 0.43 and 0.45 to 0.93, respectively, thus indicating distinct pure and simple shear dominant regimes during different stages of the evolution of the KSZ. Strain has essentially been pure shear when southern edge of the Asian plate was initially juxtaposed against the Indian plate around 70 Ma, and changed to simple shear, possibly during the reactivation of this shear zone during 21-13 Ma to produce the shear bands.

Unilateral Magma Emplacement of the Telimbela Batholith in the Central Ecuadorian Arc: Implications for Kinematics of Oblique Subduction of the Farallon‐Nazca Plate

“…The angle between ISA max and A e is ξ, and Weijermars (1991) proposed that W n = Sin2ξ (Figure 8a). The value of W n ranges from 0 to 1, and the W n values ranging from 0 to 0.75 and from 0.75 to 1 correspond to pure shear and simple shear‐dominated deformation, respectively (Roy et al., 2016).…”

“…The angle between ISA max and A e is ξ, and Weijermars (1991) proposed that W n = Sin2ξ (Figure 8a). The value of W n ranges from 0 to 1, and the W n values ranging from 0 to 0.75 and from 0.75 to 1 correspond to pure shear and simple shear-dominated deformation, respectively (Roy et al, 2016). The granitoid samples collected from the eastern part of TB contain a NE-trending, early-stage magnetic foliation, with a mean strike of N64°E oblique to the CPPF (Figure 7a); hence, ξ = 64° and W n = 0.79 (Figures 8b and 8c).…”

The Indian Subcontinent: Its Tectonics

“…(Roy et al, 2010). Kinematic vorticity (Wk) analysis along the KSZ indicate distinct pure and simple shear-dominant regimes during different stages of the evolution of the KSZ (Roy et al, 2016). Pure shear strain has affected southern edge of the Asian plate when it was initially juxtaposed against the Indian plate around 70 Ma, and changed to simple shear, possibly during its reactivation between 21 and 13 Ma.…”

Tectonics of the Western, Sikkim and Arunachal Himalaya

“…NW-SE trending dextral ductile Karakoram Shear Zone (KSZ) along the north-eastern margin of the Shyok Suture Zone (SSZ) reveals widespread augen mylonite, developed from the Tangste granite (Roy et al, 2016). To determine pure and simple shear components in the overall deformation of the KSZ, kinematic vorticity (Wk) has been estimated in 6 mylonitized granite samples, using Porphyroclast Hyperbolic Distribution (PHD) and Shear Band (SB) Analyses methods on well-developed quartz and feldspar porphyroclasts, and synthetic and antithetic shear bands, respectively.…”