Preservation of deep Himalayan PT conditions that formed during multiple events in garnet cores: Mylonitization produces erroneous results for rims

Sapkota, Jyotindra; Sanislav, Ioan V.

doi:10.1016/j.tecto.2012.10.029

Cited by 12 publications

(7 citation statements)

References 63 publications

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“…Top‐to‐the‐north shear sense indicators do occur in the Galchhi shear zone, but so do top‐to‐the‐south shear sense indicators (e.g., Figure d). Indeed, a comprehensive study of shear indicators around the Galchhi shear zone [ Sapkota and Sanislav , ] revealed both top‐to‐the‐south and top‐to‐the‐north indicators for the earliest generations of synmetamorphic and early postmetamorphic structures. Thus, although some shear sense indicators are consistent with model 3, they are also consistent with all models.…”

Section: Discussionmentioning

confidence: 99%

“…Regionally, rocks dip steeply to the south. The steepness of the foliation is commonly interpreted to result from late‐stage folding to form the ESE‐WNW trending Kathmandu syncline [ Johnson et al ., ; Gehrels et al ., ; Sapkota and Sanislav , ]. Webb et al .…”

Section: Geologymentioning

confidence: 99%

“…Garnet porphyroblasts close to the Galchhi shear zone contain inclusion trails that preserve a pre‐MCT tectonometamorphic history [ Sapkota and Sanislav , ] and record average P‐T conditions of ~11.5 kbar and ~680°C [ Johnson et al ., ; Sapkota and Sanislav , ], broadly consistent with P‐T conditions of kyanite gneiss in the Langtang region [ Kohn , ] in the footwall of the Langtang thrust. At Galchhi, P‐T estimates imply a ~150°C decrease northward toward the MCT over a structural distance of ~1.5 km.…”

Section: Kinematic Modelmentioning

confidence: 99%

“…The vast simplification of protracted and synchronous motion on the MCT and STDS with opposite shear senses [ Beaumont et al ., ] does not hold true in central Nepal. Extension in the Galchhi area is restricted to late‐stage minor normal brittle faults in the Galchhi shear zone that crosscut older deformed rocks (Figure b) [ Sapkota and Sanislav , ], and east‐west shear motion (Figure d) that possibly developed by sliding the steep southern limb of the broad anticlinorium with the growth of the Lesser Himalayan duplex system. Other klippen along the Himalaya that were emplaced on top of the Lesser Himalayan rock may have originated similarly along pre‐MCT, intra‐GHS thrusts.…”

Section: Tectonic Implicationsmentioning

confidence: 99%

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Evidence for a far-traveled thrust sheet in the Greater Himalayan thrust system, and an alternative model to building the Himalaya

et al. 2015

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The Galchhi shear zone underlies the Kathmandu klippe in central Nepal and has emerged as a key structure for discriminating competing models for the formation of the Himalayan orogenic wedge. New chronologic data from the Galchhi area suggest a new structural and orogenic interpretation. Zircons from quartzites and an orthogneiss restrict protolith deposition to between 467 + 7/ À 10 Ma and~570 Ma, with metamorphic zircon growth at 23-29 Ma. Comparable data from the Greater Himalayan Sequence (GHS) at the intra-GHS Langtang thrust, north of Galchhi, similarly restrict GHS deposition to between 475 + 7/ À 3 and 660 Ma. Undeformed pegmatites near Galchhi constrain movement of the Galchhi shear zone to ≥22.5 ± 2.3 Ma, long before slip of the Main Central Thrust in the region (≤17 Ma). Shear sense indicators in the Galchhi area indicate both top-to-the-south and top-to-the-north shears. The old age of movement, Neoproterozoic youngest detrital zircons, occurrence of top-to-the-south shear sense indicators, and intrusive Paleozoic granites, all suggest that the Galchhi shear zone is an intra-GHS top-to-the-south thrust, rather than either a thrust involving Lesser Himalayan rocks, or a top-to-the-north shear zone that juxtaposed Tethyan and GHS rocks during coeval movement of the Main Central Thrust. The GHS in Nepal was not emplaced as a single body of rock but consists of at least two ductile "thrust sheets," present in both the hinterland at Langtang and toward the foreland at Galchhi. GHS thrust sheets sequentially underplated during southward propagation of the thrust belt.

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Section: Discussionmentioning

confidence: 99%

Section: Geologymentioning

confidence: 99%

Section: Kinematic Modelmentioning

confidence: 99%

Section: Tectonic Implicationsmentioning

confidence: 99%

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Evidence for a far-traveled thrust sheet in the Greater Himalayan thrust system, and an alternative model to building the Himalaya

et al. 2015

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“…One alternative interpretation is that the Tila shear zone is a post-MCT structure associated with the formation of the Dadeldhura synform, which was passively folded by the growth of the underlying Lesser Himalayan duplex [e.g., Robinson et al, 2003Robinson et al, , 2006. Therefore, the top-to-the-north shearing along the Tila shear zone is a product of flexural slip accompanying the Lesser Himalayan duplex development [e.g., Sapkota and Sanislav, 2013]. However, our U-Pb zircon dating suggests that motion along the Tila shear zone ceased before ~17-14 Ma, whereas the Lesser Himalayan duplexing began at ~7-8 Ma [e.g., Robinson et al, 2003Robinson et al, , 2006.…”

Section: Structural Interpretations Along the Tila River Transectmentioning

confidence: 99%

Extrusion vs. duplexing models of Himalayan mountain building 2: The South Tibet detachment at the Dadeldhura klippe

Webb

Larson

et al. 2016

Tectonophysics

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Himalayan mountain building has been dominantly explained by two types of models: extrusion and duplexing. To elucidate possible roles of these mechanisms during emplacement of the Himalayan crystalline core, we investigate an area speculated to contain the southern leading edge of the crystalline core: the northeastern margin of the Dadeldhura klippe, western Nepal. We found a ~700 m thick, primarily top-to-the-north shear zone within the klippe; we term this the Tila shear zone. The shear zone occurs within a right-way-up metamorphic field gradient, and separates footwall gneiss from hanging wall schist. Similarly, deformation temperatures estimated from quartz and feldspar microstructures and quartz c-axis fabrics indicate a rightway-up thermal gradient of ~77-189 °C/km. U-Pb zircon dating of post-kinematic leucogranite dikes suggests ductile shearing along the Tila shear zone occurred prior to ~17-14 Ma. We correlate the Tila shear zone to the South Tibet detachment (STD) on the basis of consistent structural fabrics (shear sense), lithologies, metamorphism, and deformation timing. This interpretation, in combination with regional constraints, indicates southwards-increasing proximity of the STD (Tila shear zone) and the Main Central thrust (MCT). These two shear zones are separated by ~3 km of structural section in the northern portion of our study area, and become close to within ~1 km of separation, in the southern portion. Interpolation suggests that the STD (Tila shear zone) and MCT merge 15±10 km southwest of our study area. The increasing-to-south proximity and potential merger of the two shear zones suggest that the STD formed as a backthrust from the MCT. This interpretation contrasts with the long-standing normal fault interpretation of the STD. Because the STD and MCT bound the Himalayan crystalline core, these findings document crystalline core emplacement at depth via tectonic wedging. This kinematic evolution is consistent with duplexing, but not extrusion to the surface.

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Higher Himalaya in the Bhagirathi section (NW Himalaya, India): its structures, backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms

Mukherjee

2013

Int J Earth Sci (Geol Rundsch)

122

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Preservation of deep Himalayan PT conditions that formed during multiple events in garnet cores: Mylonitization produces erroneous results for rims

Cited by 12 publications

References 63 publications

Evidence for a far-traveled thrust sheet in the Greater Himalayan thrust system, and an alternative model to building the Himalaya

Evidence for a far-traveled thrust sheet in the Greater Himalayan thrust system, and an alternative model to building the Himalaya

Extrusion vs. duplexing models of Himalayan mountain building 2: The South Tibet detachment at the Dadeldhura klippe

Higher Himalaya in the Bhagirathi section (NW Himalaya, India): its structures, backthrusts and extrusion mechanism by both channel flow and critical taper mechanisms

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