Determining metamorphic grade from greenschist to amphibolite using Hyperion data: the case of an inverted metamorphic gradient of Almora nappe (lesser Himalaya)

Abstract

The intricate nature of metamorphic terrain remains a complex problem for many remote sensing scientists. The metamorphic rock assemblages are composed by intrinsic mixtures of index minerals which are defined at different pressure and temperature zones. Metamorphic assemblage’s nature and geothermal gradient can be identified using reflectance spectroscopy. The study aims to determine the nature and gradient of metamorphism using spectral identification of the index mineral phases. A model for metamorphic assemblage was developed to predict the nature and grade of metamorphism in order to address the problem with the inadequate quantification of mineral spectral mixing. The study addresses the problem by incorporating semi-empirical method of classification of metamorphic rock assemblage based on reflectance characteristics. We use the simulated spectral library of Hyperion satellite data which is favourable for classifying geological outcrops in metamorphic terrain of the Almora nappe of lower Himalayas. The Hyperion data analysis reveals the nature and trend of change of the metamorphic grades within different zones based on mass proportion of index mineral assemblages. An inverse thermal grade of the metamorphic Almora group is observed along North Almora Thrust and South Almora Thrust, where reverse thrusting might have resulted in lowering of pressure and temperature condition. The developed model can be utilized for geological survey’s involving metamorphic terrain in inaccessible areas.