Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike‐slip shear zone: The case of the right‐lateral Karakorum fault

Abstract

[1] New structural observations coupled with 15 U/Pb and 24 Ar/Ar new ages from the Karakorum shear zone (KSZ) constrain the timing and slip rate of the right-lateral Karakorum fault zone (KFZ), one of the great continental Asian strike-slip faults. In the Tangtse-Darbuk area, the Tangtse (SW) and Muglib (NE) mylonitic strands of the KSZ frame the less deformed Pangong Range. Inherited U/Pb ages show that granitic protoliths are mostly from the Karakorum and Ladakh batoliths, with a major Miocene melting event lasting from ≥21.5 to 13.5 Ma. Some of the Miocene granitic bodies show structural evidence for intrusion synkinematic to the KSZ. The oldest of these granitoids is 18.8 AE 0.4 Ma old, implying that deformation started prior to $19 Ma. Microstructural data show that right-lateral deformation pursued during cooling. Ar/Ar data show that ductile deformation stopped earlier in the Tangtse ($11 Ma) than in the Muglib strand ($7 Ma). Deformation ended at $11 Ma in the Tangtse strand while it is still active in the Muglib strand, suggesting a progressive localization of deformation. When merged with published observations along the KFZ, these data suggest that the KFZ nucleated in the North Ayilari range at least $22 Ma ago. The long-term fault rate is 0.84 to 1.3 cm/yr, considering a total offset of 200 to 240 km. The KSZ collected magma produced within the shear zone and/or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow.

Low effective fault strength due to frictional-viscous flow in phyllonites, Karakoram Fault Zone, NW India

“…Two schools of thought, based on geological evidence, exist for the long-term history of the KFZ. In one, the KFZ initiated as early as 19-32 Ma and has accommodated offsets of several hundred kilometres at slip-rates of !10 mmyr À1 (Lacassin et al, 2004;Valli et al, 2008;Boutonnet et al, 2012;Sen et al, 2014). In the other, the KFZ initiated at <16 Ma and has accumulated no more than 150 km offset at slip-rates of <10 mmyr À1 (Searle et al, 1998;Phillips et al, 2004;Wang et al, 2011;Zhang et al, 2011;Wallis et al, 2014aWallis et al, , 2014b).…”

The Xuelongshan high strain zone: Cenozoic structural evolution and implications for fault linkages and deformation along the Ailao Shan–Red River shear zone

“…The large highestrain zones are common structures in continental deformation localization, such as the active IndiaeEurasia collision zone, which accommodate amounts of total shortening, or major and longelasting structures that play a longestanding role in the lateral extrusion of crustal or lithosphericematerial (Fig. 1A, B) (Tapponnier et al, 1990;Leloup et al, 2001;Searle et al, 2010;Boutonnet et al, 2012). Elucidation of the tectonic evolution of the intraplate depends to a large degree on understanding the kinematic history of the high strain zone (Lin and Jiang, 2001).…”

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

“…The approximate timing of the event can possibly be around 70 Ma Singh, 2008, 2009). Subsequently, dextral strike-slip movement made these plates past each other; main phase of this activity occurred between 21 to 13 Ma (Phillips et al, 2004;Boutonnet et al, 2012) and has resulted in the equally dominant simple shear and has given rise to the SB fabric ( Fig. 8c).…”

“…U-Pb SHRIMP zircon analyses of the Darbuk granite and these deformed granite sheets indicate their crystallization between 20.8±0.4 and 18.0±0.6 Ma with older zircons of 671, 432, 63.0±0.8 and 45 Ma (Searle et al, 1998;Singh et al, 2007;Jain and Singh, 2008), while a major Miocene melting event lasting from ≥21.5 to 13.5 Ma is recorded along the Tangste valley ( Fig. 3d; Phillips et al, 2004;Leloup et al, 2011;Boutonnet et al, 2012) with their protoliths mainly derived from the Karakorum and Ladakh batholiths. The most recent fault movements have been identified in offsetting the levees of a debris flow and fan by 40±5 m. Concentration of 10 Be in boulders from the debris flow yields an age between 11-14 Ka, thus constraining an important phenomenon of fault reactivation during the Holocene (Brown et al, 2002).…”

“…Lacassin et al (2004), Phillips et al (2007), Rutter et al (2007), Singh (2008, 2009), Valli et al (2008), Leloup et al (2011) and Boutonnet et al (2012) have described the microstructures of these mylonites from the Pangong mountains and western Tibet in terms of their relationships to magmatism, temperature, ductile shearing and timing. These mylonites provide an excellent opportunity to study the microstructural relationships and involvement of end member strain types using the kinematic vorticity analysis.…”