Reflectance based semi-empirical model to determine nature and metamorphic grade of almora group of rocks, Kumaon (Lesser) Himalaya

Abstract

Reflectance spectroscopy can determine the nature and geothermal gradient of metamorphic assemblage. This contemplates that the spectral identification of primary mineral phase is insufficient in ascertaining the nature and gradient of metamorphism, thus, role of associated mineral phases needs to be incorporated. A series of algorithms, statistical distance mapping, spectral simulation of metamorphic assemblages from the primary spectral data has been applied to determine the nature and grade of metamorphism and isograd boundaries. The constrained randomization of (∼5500) semi-empirical simulations on single scattering albedo of the mixture components has been implemented. The model has been designed for a spectral range from 0.426 µm to 2.365 µm of hyperspectral bandwidth with RMSE of 0.09. The model was applied to field collected spectroradiometer reflectance data of Almora nappe of Lower Himalayas. An inverted thermal profile was observed along the thrust and higher grade of metamorphism was observed in the central region.