Key aspects of Himalayan geology. Morphostratigraphy, geotectonics and geomorphology in the Darjeeling Sikkim Himalaya, India / Ключевые аспекты геологии Гималаев. Морфостратиграфия, геотектоника и геоморфология Дарджилинг Сикким, Индия

The Eastern Himalaya begins in the Darjeeling-Sikkim Himalaya (DSH). It is situated between Nepal and Bhutan to the east and west, respectively. The third highest mountain on Earth, Kanchenjunga (8586 m elevation from mean sea level), is shared between Sikkim and Nepal in the west, while the Yadong-Gulu rift graben is flanked by the ridge line that forms Sikkim’s eastern boundary. The DarjeelingSikkim Himalaya’s northern limit is defined by the South Tibet Detachment (STD) system, which includes a tiny piece of the Tibetan plateau, while its southern boundary is defined by the Main Frontal fault system. To get a thematic overview, a geological map showing the arcuate stretch of the Himalaya with position of Sikkim and Darjeeling is shown in Fig. 1.1. The Himalayan border is an arc formed by the large-scale (thousands of kilometres) frontal collision between the Indian and Eurasian plates (Kellett et al. 2014). Nonetheless, the Himalayan Mountain belt exhibits smaller-scale sinuosity (hundreds of kilometres) in both its hinterland and its Himalayan front. In the Western Himalaya, the sinuosity of the Himalayan front has long been acknowledged as salients and recesses (e.g., Dehradun recess/re-entrant, Nahan salient and Kangra recess/re-entrant); more recently, the Eastern Himalaya has also been acknowledged (e.g., Dharan salient, Gorubathan recess; Mukul 2000). On the Main Himalayan Thrust or rip faults, the salient-recess transitions are commonly identified as lateral or oblique ramps (Kellett et al. 2014). The Gorubathan recess and the Dharan salient (Fig. 1.2) are the salient-recess pair across which the DSH pours. A sinistral tear fault known as the Gish Transverse Fault (GTF) characterizes the salient-recess transition.Located in the Eastern Himalayas, Sikkim is a small state in India covering 7096 km2. Due to the tectonic complexity, polyphase metamorphism and unfossiliferous nature of the majority of the lithounits, the stratigraphic locations and geological set-up of the rock strata in the Sikkim Himalaya are subjects of scholarly dispute, assessment and re-evaluation. The state’s geological formations are arranged in reverse tectonic sequence from south to north. The majority of Sikkim’s Outer Himalaya is covered by the Lesser Himalaya. The Tethyan Himalaya encompasses the northernmost regions of Sikkim and includes Phanerozoic deposits. An essential geological component of Sikkim Himalaya is Darjeeling Himalaya. The major geological and physiographical aspects of Darjeeling district of West Bengal state and Sikkim state are inextricable with many unavoidable reptations and cross references, and therefore, to provide clarity, geological homogeneity and continuity, the geology of these two sectors of Himalaya, are presented together in this book. There is a composite study area map of the Darjeeling-Sikkim Himalaya (Fig. 1.3).<...>