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1 Map of Main Central thrust and Greater Himalayan sequence localities in the Gangtok-Mangan section, inset shows location of section in NE of Sikkim. The upper boundary of the MCT high strain zone is positioned at the protolith boundary of Mottram et al. (2014). Metamorphic isograds are shown as dotted and dashed lines. The extent of the zone of deformation associated with the MCT is shown as the hatched zone.
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The Darjeeling-Sikkim Himalaya marks the beginning of the Eastern Himalaya. It is located between Bhutan to the east and Nepal to the west. In the west Sikkim shares Kanchenjunga, Earth’s third highest mountain, with Nepal, while the ridge line forming Sikkim’s eastern border flanks the Yadong-Gulu rift graben. The South Tibet detachment (STD) syst...
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India–Asia collision resulted in crustal thickening and shortening, metamorphism and partial melting along the 2200 km-long Himalayan range. In the core of the Greater Himalaya, widespread in situ partial melting in sillimanite+K-feldspar gneisses resulted in formation of migmatites and Ms+Bt+Grt+Tur±Crd±Sil leucogranites, mainly by muscovite dehyd...
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... Further, the rainfall data collected from local stations revealed most of the annual rainfall precipitates within the months of June to August. Considering the seismic zonation map of India (BIS-2002), this area falls in high seismic zone IV. Kellett et al. (2014) studied the seismicity pattern of Darjeeling-Sikkim Himalaya and predicted a great impending earthquake of > 7 M w . The lithology of the area is tailored by shear zones with thrust and faults like tectonic features. ...
... For this study, the derived slope map shows a range of 0° to 79° and based on that it is categorized into five subclasses (Fig. 5a). Similarly, in hilly terrain, micro-climatic conditions followed by density of vegetation cover are significantly governed by the slope aspect which indirectly plays an important role in landslide process (Chen et al., Acharyya (1980), Gangopadhyay (1995), Kellett et al. (2014), Mukul et al. (2017), Patra and Saha (2019) 1:50,000 to 1:2,50,000 Lithology, thrust and fault proximity 2019). The obtained slope aspect map of this area is attributed to nine subclasses (Fig. 5b). ...
Landslides are significant and recurring hazards in the Himalayan region, necessitating the need for landslide susceptibility zonation (LSZ) to identify landslide probable areas. This study applied three bi-variate models namely certainty factor (CF), evidential belief function (EBF), and weight of evidence (WofE), with two soft-computing models, namely artificial neural network (ANN) and random forest (RF) to predict landslides in parts of the Kalimpong region. Ensembles combining soft-computing and bi-variate models were examined and compared with traditional bi-variate models for LSZ prediction accuracy. To improve ANN and RF model performance, three non-landslide scenarios were also assessed. Nine model architectures (CF, EBF, WofE, ANN-CF, ANN-EBF, ANN-WofE, RF-CF, RF-EBF, RF-WofE) were designed to derive landslide susceptibility index (LSI) values. These LSI values were classified into five susceptible zones using the success rate curve method derived class boundaries. Model prediction performance was evaluated using the area under curve (AUC) of receiver operating characteristic curve, standard error (SE), 95% confidence interval (CI), and chi-square (χ2)-based measures. The results indicate ensemble models achieved better prediction accuracy (average AUC of 0.834) compared to bi-variate models (average AUC of 0.815), with RF-CF (AUC = 0.843, SE = 0.0092, 95% of CI = 0.825 to 0.862, and χ2 = 1478.61) and ANN-CF (AUC = 0.842, SE = 0.0093, 95% of CI = 0.824 to 0.860, and χ2 = 1435.89) models outperformed all. Additionally, the assessment found ~ 34% area is highly susceptible to landslides. It is envisaged that the present attempt will be helpful for better land use planning in the investigated area.
... Hence the Sikkim Himalayan leucogranite bodies remain an understudied gap in the record of Himalayan melt generation. Moreover the abundance of previous geochronological constraints from the surrounding Tethyan Himalayan Sequence (THS), HHS and LHS rocks (Catlos et al., 2004;Rubatto et al., 2013;Anczkiewicz et al., 2014;Kellett et al., 2014;Mottram et al., 2014a,b) provided the ideal context for new geological investigations into the source and emplacement mechanisms of Himalayan leucogranites. This paper aims to provide a new petrological, geochemical and geochronological dataset of leucogranites from the Sikkim Himalayas. ...
... Initial geological mapping in the Sikkim Himalayas was carried out by Mallet (1875), that was later modified by (Auden, 1935;Heim and Gansser, 1939;Wager, 1939;Ghosh, 1952;Gansser, 1964). Since then, numerous studies have used structural analysis, geological mapping, geochronological, geothermobarometric and petrological study to understand the tectono-metamorphic evolution of this region (Catlos et al., 2004;Harris et al., 2004;Kellett et al., 2014;Mottram et al., 2014aMottram et al., , 2015aSorcar et al., 2014;Bhattacharyya et al., 2015;Srivastava et al., 2022). The present study has been carried out in North Sikkim (Fig. 2) and the Darjeeling Hills to the south (Fig. 2) which lie in the eastern Himalayas as part of the HHS. ...
... The present study has been carried out in North Sikkim (Fig. 2) and the Darjeeling Hills to the south (Fig. 2) which lie in the eastern Himalayas as part of the HHS. The Sikkim HHS is dominated by the upper amphibolite-granulite facies Kanchenjunga-Darjeeling gneiss, composed of calc-silicates, leucogranites, migmatites, sillimanite-kyanite bearing mica schist and biotite gneiss (Rubatto et al., 2013;Kellett et al., 2014;Bhattacharyya et al., 2015). ...
Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular. This paper aims to understand the melt source and emplacement age of the leucogranites from Sikkim in order to decipher the deep geodynamic processes of the eastern Himalayas. Zircon U-Pb analysis of the Higher Himalayan Sequence (HHS) metamorphic core reveals a prolonged period of crustal melting between >33 to ca. 14 Ma. Major and trace element abundances are presented for 27 leucogranites from North Sikkim that are classified into two-mica and tourmaline leucogranite types. They are peraluminous in composition, characterized by high SiO2 (70.91–74.9 wt.%), Al2O3 (13.69–15.82 wt.%), and low MgO (0.13–0.74 wt.%). Elemental abundances suggest that Sikkim Himalayan leucogranites are derived from crustal melts. The two-mica leucogranites are derived from a metagreywacke source, whereas the tourmaline leucogranites are sourced from metapelitic sources, with inherited zircons indicating an HHS origin for both types. U-Pb zircon geochronology of the two mica leucogranites indicates ages of ca. 19–15 Ma, consistent with crustal melting recorded in HHS gneisses from Darjeeling. Monazites from both the two-mica and tourmaline granites yield a crystallization age of ca. 14 Ma, coeval with movement on the Main Central Thrust and South Tibetan Detachment System which further provides constraints on the timing and mechanism of petrogenesis of leucogranites in the Sikkim Himalayas.
... The Greater Himalayan Sequence (GHS) and the TSS are separated by the extensional STD, which was active in the Early-Middle Miocene (Burchfiel et al. 1992;Kellett et al. 2013). In Sikkim Himalayas, between two branches of the MCT, lies a heavily sheared zone known as the Main Central Thrust Zone (MCTZ) (Bhattacharyya and Mitra 2009;Kellett et al. 2014). The Lesser Himalayan Sequence (LHS), which is exposed in the Teesta tectonic half-window, is made up of greenschistfacies meta sedimentary rocks and is found in the footwall of the MCTZ (Abrahami et al. 2016). ...
Bedrock landslides are the primary agent of hillslope erosion, and mass wasting, and an essential source of sediment flux to the fluvial network in the mountainous terrain, in particular, in the Himalayan mountain belt. To understand the characteristics of the landscape, we calculate geomorphic matrices including the topographic variables, longitudinal and topographic swath profile, channel steepness index, and stream length gradient index to analyze the spatial distribution of landslide occurrences over landscape evolution. The intensity of rainfall gradient and topographic variables were spatially correlated with the erosion and exhumation rates of the studied catchment. Our analysis suggests that the zones with slope ranges of 24°–28°, relief ranges of 800–1000 m, and elevation ranges of 1500–1700 m, which coincide with the rainfall intensity range of 2500–2700 mm/year in the Teesta river catchment, have the highest probability of frequently occurring landslides. Higher tectonic activity is principally responsible for the landslide over the Higher Himalaya to the north of the Main Central Thrust (MCT)–Main Boundary Thrust (MBT) along the orographic barrier. In contrast, litho-tectonics regulates and mostly triggers landslides adjacent to the MCT–MBT structural affinity dominated by rainfall intensity. Our observation suggests that erosion rates frequently exceed long-term exhumation rates and are spatially more variable. Moreover, they exhibit significantly divergent spatial patterns, which suggests that the processes governing these rates are independent. Exhumation rates have been shown to decrease from south to north over geological periods, rising in the southwest region at ~ 1.2 mm/year and decreasing to ~ 0.5 mm/year in the northernmost region of the Teesta catchment. Long-term exhumation rates are not correlated with geomorphic or climatic variables. The highest apparent erosion rates (5 mm/year) are seen in the catchment that crosses the MCT Zone, however, these rates appear to have been severely impacted by recent landslides. Conversely, changes in rainfall rate do not appear to significantly impact either rate of long-term exhumation or erosion in the Teesta catchment.
... 15 m spatial resolution Landsat-8 OLI satellite images ( https:// earthexplorer.usgs.gov/), soil map collected from National Bureau of Soil Survey and Land Use Planning ( NBSSLUP) and the regional geological information collected from different literature database ( after Acharyya 1980;Gangopadhyay 1995;Kellett et al. 2014;Mukul et al. 2017;Patra and Saha 2019). All the collected datasets are processed in a 25 m × 25 m raster resolution using ESRI ArcGIS and for modeling and validation, Microsoft Excel and R Studio platforms are used. ...
... For this study, different geological factors including lithological setup, lineament proximity, soil texture information, thrust/ faults proximity have been used and are presented in Figure 6g-j. In the lithology map spatial extent of rock boundaries are delineated based on the reference map given by Gangopadhyay ( 1995) and was further updated using other the literature information ( Acharyya 1980;Kellett et al. 2014;Mukul et al. 2017;Patra and Saha 2019). Moreover, during filed survey the prepared map was cross-checked and the final map contains six major formations ( Figure 16.6g). ...
... The Southern Singalila range, being a part of the Lesser Himalayan Duplex (LHD), exhibits rock structure (Mukul, 2010) involving the Daling, Buxa, and Gondwana rock sequences (Kellett et al., 2014). The Darjeeling group of rocks is the oldest formation consisting of high-grade gneiss which is known as Darjeeling gneiss containing quartz and feldspar. ...
... The GHS is a continuous belt of medium to high-grade metasedimentary and metaigneous rocks from the Paleoproterozoic to the Ordovician (1800-480 Ma) and associated leucogranites (LeFort 1975;Hodges 2000;Montomoli et al. 2015;Yin 2006). In Sikkim, GHS consists of high-grade pelitic rocks, calc-silicates, leucogranites, pegmatites, gneissic rocks, migmatites, sporadic quartzites and metabasites which MCT separates from Lesser Himalayan Sequence comprising low-grade metamorphic rocks (Neogi et al. 1998;Dasgupta et al. 2004;Kellett et al. 2014;Joshi et al. 2021b). Along with the formation of leucogranites, anatexis, migmatization and granulite facies metamorphism, the GHS has experienced a long history of ductile deformation (Kellett et al. 2014). ...
... In Sikkim, GHS consists of high-grade pelitic rocks, calc-silicates, leucogranites, pegmatites, gneissic rocks, migmatites, sporadic quartzites and metabasites which MCT separates from Lesser Himalayan Sequence comprising low-grade metamorphic rocks (Neogi et al. 1998;Dasgupta et al. 2004;Kellett et al. 2014;Joshi et al. 2021b). Along with the formation of leucogranites, anatexis, migmatization and granulite facies metamorphism, the GHS has experienced a long history of ductile deformation (Kellett et al. 2014). The STDS is a low-angle normal fault that separates high-grade rocks of GHS from slates and sandstones of Tethyan sedimentary sequences, and MCT distinguishes GHS in the hanging wall from LHS in the footwall (Kellett et al. 2014). ...
... Along with the formation of leucogranites, anatexis, migmatization and granulite facies metamorphism, the GHS has experienced a long history of ductile deformation (Kellett et al. 2014). The STDS is a low-angle normal fault that separates high-grade rocks of GHS from slates and sandstones of Tethyan sedimentary sequences, and MCT distinguishes GHS in the hanging wall from LHS in the footwall (Kellett et al. 2014). The MCT in Sikkim is a ductile zone that shows inverted metamorphism from garnet to sillimanite grade with strain distribution over many kilometres (Harris et al. 2004). ...
The pegmatites present near the Yumthang Valley, North Sikkim, intruding the Higher Himalayan Crystallines Sequences (HHCS), consists of columnar tourmaline aggregates forming radial structures. We discuss the bulk major, trace including Rare Earth Elements (REEs) data of the pegmatites and Boron isotope data from the pegmatitic tourmalines near Yumthang Valley, North Sikkim, in the present contribution. The studied pegmatites have high SiO2 (67.83-75.35 wt.%), Al2O3 (14.58-17.51 wt.%), K2O (4.67-6.12 wt.%) and A/CNK values ranging from (1.18-1.40). The normative corundum (>1%) and peraluminous nature of the studied pegmatites indicate their S-type granitic parentage for these pegmatites. Based on limited geochemical studies, the studied pegmatites have been divided into two groups viz. Type 1: which are more fractionated having [(La/Yb)N from (4.27 to 8.73 )] and have a higher content of total REE and Type 2: having [(La/Yb)N from (1.88 to 6.63)]. The δ11B values of the studied pegmatitic tourmalines are similar to that of the continental crust and S-type granites and ranges from −13.83 ± 0.37 ‰ to −12.78 ± 0.84 ‰ suggesting crustal origin. The low 11B values from the studied tourmalines suggest derivation at a later stage and may result from fractionation during magmatic degassing from magmatic-hydrothermal fluids.
... This imbrication has raised the bed of the river Tista leading to the formation of a bar upstream (Fig. 4) (Valdiya 1976). The Lesser Himalayan Duplex is an active structure in the Darjeeling Sikkim, Himalaya with a very pronounced cluster of earthquake epicentres (Kellet et al. 2014). The clustering is prominent along the traces of surface exposures between MCT and MBT (Pandey et al. 1999). ...
... The clustering is prominent along the traces of surface exposures between MCT and MBT (Pandey et al. 1999). The observed seismicity in the Lesser Himalayan Duplex is dominated by moderate frequent thrust and strike-slip earthquakes (Kellet et al. 2014) whereas eastern Nepal records moderate to micro earthquakes along the entire length of Himalayan Wedge (Pandey et al.1999;de la Torre et al. 2007). ...
Neotectonics keeps its prominent signatures on river channel evolution. This chapter reviewed emergence, flourishment and advancement of the study of neotectonics, adjustment of fluvial forms and processes to neotectonics within the territory of Indian Subcontinent. Based on this review, we confirm the theme of the volume and suggest profuse scope of further research on Neotectonic Movements and Channel Evolution in the Indian Subcontinent ranging from basin-scale to channel-site scale. We also introduced other chapters of the book.
... They proposed a regional rainfall threshold that distinctly indicates high-intensity short duration monsoonal rainfall events are the foremost triggering factor for landslides in this region. Apart from this Kellett et al. (2014) shows the Darjeeling-Kalimpong region is seismically very active and highly susceptible to earthquakes. In 2011, a 6.9 ( M w ) shallow focus (19.7 km depth) earthquake occurred in the Sikkim-Darjeeling region that reactivated few old slides and initiated many new slides in some areas that have no past records (Chakraborty et al., 2011). ...
... The lithology map of the Kalimpong region has been prepared from the geological map of the Darjeeling-Sikkim region (Gangopadhyay, 1995). Further, based on the literature survey and limited field checks the prepared map was updated (Acharyya, 1980;Kellett et al., 2014;Mukul et al., 2017;Patra & Saha, 2019) and the spatial extent of different rock types is outlined (Fig. 6g). The map shows six major formations namely, Siwalik, Barakar, Talchir, Gorubathan, Reyang-Phuntsholing and highly metamorphosed Pre-Cambrian formation comprising of sandstone, conglomerate, limestone, shale, schist, etc. ...
... The density distribution indicates northern and north-western parts have high drainage density due to the presence of a large number of closely spaced lower-order drainage channels. (AfterAcharyya, 1980;Gangopadhyay, 1995;Kellett et al., 2014;Mukul et al ...
Landslides are one the most destructive and life-endangering hazard in the Darjeeling Himalayan region and keeping in mind the interest of society and their future prospects identification of landslide potential areas is a very pertinent task in this area. Therefore, the present study aimed toward the landslide susceptibility zonation (LSZ) mapping in and around the Kalimpong region by applying Analytic Hierarchy Process (AHP) method integrated with fifteen causative factors including slope, lineament, drainage density, land use land cover, relative relief, soil texture, lithology, elevation, aspect, thrust and faults, plan curvature, profile curvature, road network, topographic wetness index and stream power index. Tolerance and variance inflation factors with Pearson's correlation coefficient are used to assess potential collinearity among the selected factors, and subsequently, the final model has been constructed by enduring an acceptable consistency ratio (<0.10). Thereafter, to classify this region into very low, low, moderate, high and very high susceptible zones quantile, geometric interval, Jenk’s natural break and success rate curve (SRC) techniques are adopted to compare and check the optimum LSZ categorization. Considering the identified 647 landslides, Area Under Curve (AUC) of Receiver Operating Characteristic (ROC) curve is used to gauge the best LSZ map. The AUC ROC shows SRC method (m = 0.9) yields the highest result, achieving a prediction accuracy of 79.5% and, therefore, is considered the most promising LSZ form for the present study area. The results obtained from the study highlight the spatial information of areas that may face slope instability and helps government agencies, stakeholders for drafting adequate measures due to absence of proper landslide early warning systems in this region.
... Ghosh (1952) examined that Gondwana rocks as exposed from older Buxa and Daling rock as a window. O t h e r t h a n t h e a b o v e w o r k m a n y r e s e a r c h e r s l i k e R a i n a ( 1 9 8 2 ) , Acharya(1971Acharya( ,1982Acharya( ,1989, Roy(1971), Sinha Roy(1974, Ray(1975Ray( ,1976Ray( ,1989, A c h a r y y a a n d R a y ( 1 9 8 9 ) , Mukhopadhyay(1979), Paul et al.(1982, S r i k a n t i a ( 1 9 8 9 ) , M a t i n a n d Mazumdar(2009), Basu(2012), , Ghosh et al.(2018), Kellett et al.(2014), Mukhopaddhay et al.(2017, Parui and Bhattacharyya(2018), Bose and Mukherjee(2019) have also studied the geology and evidence of tectonic activity of this region in detail. Drainage systems evolve primarily influenced by underlying rock structures as witnessed in the Rangit river basin. ...
The geology and tectonics of an area play a very important role in the development of geomorphic features and drainage of a region. The Rangit River Basin is a part of Sikkim-Darjeeling Himalaya that contains very significant geological and tectonic characteristics. The basin has mainly three rock groups that are Central Crystalline Complex, the Daling group and the Gondwana group. The spectacular feature of this basin is Rangit Window, where the underlying Gondwana rock group is exposed from overlaying Daling group. Rangit basin exhibits both folded and fault structures which are indeed unique. A detailed study of litho-tectonic setup as well as to identify geomorphic features of this basin geological maps from of Geological Survey of India and topographical maps from Survey of India along with tectonic maps and secondary data have been used. This study is an attempt to show the relation between litho-tectonic setup and drainage development. The river basin is the product of morphotectonics and morphoclimatic mechanisms. Evidence of the faulting, folding, thrusting, fractures and cracks as a witnessed on-field point to the influence of neo-tectonism episodes have been noticed in the study area. Some micro landform features have also been identified after extensive fieldwork in the study area. The present study is an attempt to understand the significant role of rock structure in drainage development in the study area.
... The South Tibetan detachment (STD) system marks its northern boundary and the Main Frontal Thrust (MFT) system defines its southern boundary (Fig. 1). The Main Boundary Thrust (MBT), the Ramgarh Thrust (RT, also known as Daling Thrust-DT or North Kalijhora Thrust-NKT) and the Main Central thrust (MCT) are other major EW striking thrusts that control structuration, geomorphology and kinematics in this region (Mukul, 2000;Kellett et al., 2014). The RT and MBT thrust sheets are piled up and give rise to a complex geometry and form the Lesser Himalayan Duplex (LHD). ...
... The LHD and the Kangmar (Fig. 1) anticline are assumed to provide critical taper that control the propagation of the thrust sheets towards the foreland (Decelles and Mitra, 1995;Mukul, 2000Mukul, , 2010Mitra et al., 2010). The MCT Zone is characterized by inverted metamorphic isograds and is assumed to be active in a longer timescale like the MBT where the fault plane is folded and inverted (MOHAN et al., 1989;Neogi et al., 1998;Catlos et al., 2004;Dasgupta et al., 2004;Harris et al., 2004;Searle and Szulc, 2005;Gupta et al., 2010;Anczkiewicz et al., 2014;Kellett et al., 2014;Mottram et al., 2014a;2014b;Gaidies et al., 2015;Landry et al., 2016). Out of sequence, neotectonic thrusts between the MBT and South Kalijhora Thrust (SKT) and the LHD are the two most active regions in the Darjeeling-Sikkim Himalayas as inferred from the kinematic analysis and the preferred localization recent earthquake epicenters (Mukul et al., 2007;Mukul, 2010). ...
This paper presents a study where Fracture Induced Electromagnetic Radiation (FEMR) technique has been used to decipher the direction of recent near-surface stresses along the near surface segments of the major thrusts of the Darjeeling-Sikkim Himalaya, India. Slip Tendency analysis on the same thrust system was carried out where the sensitivity of the mutual angle between thrust strike and stress azimuth was tested. A major realignment of the regional surface stress was observed in specific areas of the Darjeeling-Sikkim Himalaya which perhaps indicate enhanced localized neotectonic activities. An attempt was made to test spatial correlation between landslide locations and areas with enhanced tectonic activity as predicted by the FEMR technique. We conclude that the newly practiced FEMR technique can be a fruitful shallow activity indicator of critically stressed fault systems which could cause shallow earthquakes and landslides.
