No abstract

The abundance of garnet-biotite pair in a wide range of rocks mainly from upper green schist to granulite facies has made it one of the most widely used pairs for estimation of temperature at which once rocks equilibrated. In last four decades, more than 20 thermometer models of garnet-biotite pair have been proposed. To find the suitability of models, twenty-one thermometers formulated by a number of scholars since 1976 is considered. 27 sample data of granulites from the global literature were collected and processed through the “Gt-Bio.EXE” software. We conclude that four models are the most valid and reliable of these kinds of thermometers: Perchuk and Lavrente’va (1983); Thompson (1976); Ferry and Spear (1978) and Holdaway and Lee (1977).

Amphiboles are frequently observed in the medium to high grade metamorphic rocks of garnet bearing amphibolites from Thana. In present work, authors have discussed the mineral chemistry and nomenclature of amphiboles. On the basis of mineral chemistry, the amphibole from garnet bearing amphibolite are normally varies from Hastingsite, Ferropargasite to Tschermakite variety.

Phyllites from Patharkhola, Lesser Kumaun Himalaya have been studied to investigate the geochemical characteristics of these rocks and their formation processes and mechanism of emplacement. Petrographically, phyllites have been showing the mineral assemblages as Biotite (25% approx.)-chlorite (25% approx.)-muscovite (20% approx.)-quartz (10% approx.)-feldspar (10% approx.)-sericite (5% approx.). Geochemically, the analysed four samples of phyllites have high SiO2 and Al2O3 values. Phyllites with higher alumina have more enrichment of trace elements. The enrichment of Zr and depletion of Y and Nb indicate preferential survival of zircon in extreme weathering conditions. The HFSE has shown variation in the ratios due to decoupling with the major oxides. The enrichment of LREE and depletion of HREE suggest mixing of the terrigenous sediments with the concominant magma. Discrimination plots to classify the tectonic settings suggested that the phyllites of Patharkhola have formed in active continental margins.

The Patharkhola area (longitude 79°09'E to 79°17'56''E and latitude 29°47'42''N to 29°56'69''N) covering an area of about 125 square Kms situated in Almora District,  Uttarakhand forming a part of the Almora Nappe has been selected for the detailed geological mapping at an scale of 2 cm equal to 1 Km. The rocks mainly include phyllites, schists and gneisses forming an anticlinal structure showing phyllites in the NW, S to SW and in the western part of the area, while the schists occur in the folded outcrop pattern in between both the limbs of the fold and the gneisses occur in the core of the fold. Although thin quartzitic bands has also been noticed interbedded with phyllites and schists. Several transverse faults have been noticed in the area under investigation which has been demarcated in the map. Bulletin of Department of Geology, vol. 20-21, 2018, pp: 1-6