Structural and thermal evolution of the South Tibetan Detachment shear zone in the Mt Everest region, from the 1933 sample collection of L. R. Wager
Published:April 17, 2019
David J. Waters, Richard D. Law, Michael P. Searle, Micah J. Jessup, 2019. "Structural and thermal evolution of the South Tibetan Detachment shear zone in the Mt Everest region, from the 1933 sample collection of L. R. Wager", Metamorphic Geology: Microscale to Mountain Belts, Silvio Ferrero, Pierre Lanari, Philippe Goncalves, Eugene G. Grosch
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Microstructural and petrological data from >60 samples, collected by L.R. Wager in 1933, have been used alongside existing data to investigate temperature gradients and deformational style in four profiles across the South Tibetan Detachment shear zone, over a north–south distance of 35 km in the Mt Everest area, east-central Himalaya. The ductile shear zone, defined on petrographic criteria, extends for c. 900 m beneath the brittle Qomolangma Detachment (QD). New thermobarometry from the north flank of Mt Everest reveals a gradient from 440°C at the QD down to samples recording peak conditions around 650°C, 5.5 kbar. The upper limit of leucogranite sheets forms an approximately isothermal surface at 600–650°C within the developing shear zone. The recrystallized grain size of quartz shows a systematic increase down-section in four transects. Profiles of deformation temperature reveal gradients of up to 200°C km−1 whose formation and preservation required a combination of processes: a shear zone active for a short period (≤18–15.5 Ma) at high strain rates, with a component of vertical shortening, and a contribution of latent heat from emplacement of sheeted granites. The likely horizontal displacement was >40 km, with up to 10 km of vertical exhumation.
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Metamorphic Geology: Microscale to Mountain Belts
CONTAINS OPEN ACCESS
In Earth evolution, mountain belts are the loci of crustal growth, reworking and recycling. These crustal-scale processes are unravelled through microscale investigations of textures and mineral assemblages of metamorphic rocks. Multiple episodes of metamorphism, re-equilibration and deformation, however, generally produce a complex and tightly interwoven pattern of microstructures and assemblages. Over the last two decades, the combination of advanced computing and technological capabilities with new concepts has provided a vast array of novel petrological tools and high-resolution/high-sensitivity techniques for microanalysis and imaging. Such novel approaches are proving fundamental to untangling the enigma represented by metamorphism with an unprecedented level of detail and confidence. As a result, the first decade and a half of this century has already seen the tumultuous development of new research avenues in metamorphic petrology. This book aims to provide a timely overview of the state of the art of this field, of newly developed petrological techniques, future advancements and significant new case studies.