Скачать или смотреть Development and Application of High-Resolution Garnet P-T-t paths to Himalayan Tectonics E.J. Catlos

Development and Application of High-Resolution Garnet P-T-t paths to Himalayan Tectonics

Catlos, E.J., Etzel, T.M., Dubey, C.S.
Tectonic models as a universal outcome generate predictions regarding the travel-time paths of rocks as they displace due to the application of particular input parameters and boundary conditions. A need for most of these models, either as a constraint for realistic input conditions or to gauge their relevance to a particular natural system, is pressure‐temperature‐time (P‐T‐t) paths from individual rock samples that track the conditions they experienced during displacement. This type of information is a valuable addition to microstructural data regarding strain recorded during rock deformation. Zoned garnets have long been used to generate P‐T paths. However, low‐resolution paths are limited in their ability to test ideas regarding lithospheric response to perturbations. Thermodynamic modelling [1-3] allows the ability to generate high‐resolution P‐T paths that show the conditions responsible for garnet growth within major Himalayan fault systems exposed across fault systems in central Nepal (Darondi Khola and Marysandi River) and NW India (Bhagirathi River) [4,5]. The Main Central Thrust (MCT) separates lower-grade garnet-bearing schists from the Lesser Himalayan Formation from higher-grade gneisses of the Greater Himalayan Crystallines. MCT footwall P-T paths are consistent with shear zone imbrication and demonstrate consistency in conditions across the footwall at locations ~650 km apart. Lesser Himalayan garnets seem ideally suited for the approach and appear to behave as closed systems with minimal modification since growth. High-resolution paths can significantly increase the understanding of the dynamics of field areas that contain garnet.
Isochemical phase diagrams with garnet core isopleths (colored bars) and P-T paths (black lines) from Himalayan MCT footwall garnets collected from the (a) Bhagirathi River, (b) Darondi Khola, and (c) Marysandi River [see also 4,5].