ANNOUNCEMENTS
Reflectance spectroscopy can be utilised to determine the nature and geothermal gradient of metamorphic assemblages. The spectral identification of primary mineral phase alone is insufficient in ascertaining the nature and gradient of metamorphism. To address the inadequacy of quantification of mineral spectral mixture, a model has been developed for metamorphic assemblage to predict the nature and grade of metamorphism. Considering an intrinsic mixture of metamorphic minerals, a series of algorithms based on the reflectance data has been applied to delineate isograd boundaries. Semi-empirical simulations on single scattering albedo of the mixture components have been implemented after constraint randomisations. The model has been designed for a spectral range of hyperspectral image (Hyperion). The model was subjected to the reflectance data of the metamorphic outcrops along the Almora nappe, Lesser Himalaya. The simulated spectral library was subjected to spectral mapping with hyperspectral data. Hyperion satellite data whose higher spectral resolution is favourable for classifying geological outcrops in metamorphic terrain was used to map the metamorphic gradient of the Almora nappe of lower Himalayas. The image analysis reveals the nature and trend of change of the metamorphic grades within different zones. An inverse thermal grade of the metamorphic Almora group is observed along North Almora Thrust and South Almora Thrust. The inverted thermal profile is attributed to the associated thrust mechanism along with igneous intrusion. The quantitative data for metamorphic mineral assemblage from reflectance data can be used as bulk chemistry data for mineral assemblage. The data is used in numerical modelling of the phases in pressure-temperature (P-T) space using pseudosection approach. The phase-composition relation in the P-T dimension provides the relation among the identified phases and the constraints among the mixture of the endmembers. The correlation of the spectral result with the observed data from the conventional method shows the possibility of reflectance-based studies for geothermobarometric modeling.
