Langtang Area Research Articles

A Study on Temporal Variation of Snow and Glacier in Langtang Basin

Snow cover and glacier in the Himalaya play a major role for generating stream flow in South Asia. It is already observed that the snowline is retreating in the Himalaya region. While there are relatively more studies on glaciers fluctuation in this region, studies on snow cover are relatively rare. Present study is aimed to analyze the temporal variation of snow and glacier cover (both debris and clean ice covered) of Langtang area within the catchment 432.32 sq.km at outlet 28°12'10.78"N and 85°27'44.58"E. Currently, we used intermittent medium resolution satellite imageries (Landsat) to study the fluctuation in snow cover and glacier area in the Langtang catchment. Our analysis revealed that the glaciers in the study area are tentatively shrinking in average. More specifically, the Landsat Satellite images of the concerned area processed through ERDAS Imagine and their detailed analysis conducted in ArcGIS show that the minimum snow coverage area is declining and maximum snow coverage is in the average range and in the case of debris coverage glacier and clean ice glacier, the trend is declining. The novelty of this study was to develop a robust process having potentiality to predict snow coverage that would be ultimately applicable to agricultural sectors.

PRELIMINARY INVESTIGATION OF THE CHEMICAL QUALITY OF DOMESTIC WATER SOURCES IN SELECTED COMMUNITIES OF LANGTANG AREA, PLATEAU STATE, NIGERIA

A preliminary analysis of the chemical quality of domestic water sources in Langtang area was undertaken to determine variation in quality of water sources and how it meets the Nigerian Standard for Drinking Water Quality (NSDWQ). Using stratified random sampling technique, 50 water samples were taken from five different sources: rain, dams, streams, boreholes and hand dug-wells. Samples were tested in the laboratory for 20 parameters using standard methods described by USEPA (2012) and results subjected to ANOVA and independent sample t-tests. Temperature (28), turbidity (15), Ca (85), Mg (30), Cl (275), Fe (1.2), Pb (0.1) and Cd (0.002) had average mean above limits. ANOVA result shows significant variation in water quality with p-value of 0.001. Post-Hoc test revealed significant variation in 80% of the parameters tested: temperature, turbidity, EC, CaCO3, F, TDS, Ca, Mg, NO3, Fe, Cu, Al, Pb, As and Cd. Only pH, Cl, Mn, Cr and Zn do not show significant variation. Independent sample t-test also show significant variation in water quality to the Nigerian Standard for Drinking Water Quality (NSDWQ), which implies the water is unsuitable for human consumption. This study has demonstrated that despite differences in the protection levels of water sources, some parameters may still be the same across sources. It is therefore recommended that detail analysis of each water source be carried out to identify parameters responsible for pollution, as well as remediation the of water before consumption.

Annotated checklist of Collembola of Nepal

This is the first annotated checklist of Collembola species of Nepal. It includes 167 collembolan species belonging to 78 genera and 17 families including 45 endemic species. Majority of the Nepalese collembolan species were reported from major trekking routes viz. Mount Everest, Annapurna Conservation Area and Langtang area with very few other locations. The highest record of collembola in Nepal is about 5800 m asl. Southern Terai and Siwalik range remain unexplored.

Thanatology Tourism in Nepal Himalayan Region: A Case of Langtang

On 25th April 2015 at 11:56 am local time, a devastating earthquake measuring 7.8 on the Richter scale shook Nepal. It is considered as one of the most fatal disasters in Nepal, ensuing aft restocks; avalanches and landslides triggered in the aftermath killed over 9,000 people. The most damage occurred when the earthquake triggered a destructive avalanche composed of ice, snow and soil, burying the entire Langtang village- a huge settlement of the popular adventure tourism destination of Nepal and killing at least 253 people. This study envisions to explore the scopes of special-interest dark (thanatology) tourism in the post-disaster scene, and it is used as a vehicle for self-reflection and education. This paper also explores the tourism prototype for an adventure tourism destination that has been severely impacted by a disaster. The paper adapts sociological theory, experience, and participant observation to complete a vanity ethnographic study of a “post-disaster tour” in the Langtang area. The tools and techniques of data collection derived from qualitative methodological approaches such as case study, semi-structured interviews, informal interviews, participant observation, content analysis, focus group discussions, in-depth interviews and house to house visit. The findings show how the adventure tourism hosts bounced back and depicted resiliency through unified reconstruction. Langtang’s post-disaster touristic setting instigates a unique paradigm in the tourism sector that can go parallel with the adventure tourism engagements. Th e model is represented through the amalgamation of dark tourism (Dark) and adventure tourism (Adventure), which forms a phenomenon that is named “darventure” (Kunwar, 2019) tourism. The‘ darventure’ tourism features the elements of both thanatology and frontier thrills at the same place. Dark tourist and adventure tourist experiences can coexist in Langtang, it creates a unique tourism prototype that complements both practices and can be offered as ‘darventure’ tourism.

Protolith lithostratigraphy of the Greater Himalayan Series in Langtang, Nepal: implications for the architecture of the northern Indian margin

Abstract Reconstruction of the protolith lithostratigraphy of amphibolite-facies metasedimentary rocks of the Greater Himalayan Series (GHS) in Nepal documents a single, long-lived passive-margin succession that was deposited along the northern margin of the Indian Craton. In the Langtang area, Paleoproterozoic gneisses are unconformably overlain by a succession of upper Neoproterozoic–Ordovician fluvio-deltaic quartzite, basinal pelite and psammitic beds that grade upsection into micaceous semipelite and pelite. U–Pb zircon geochronology yields maximum depositional ages between c. 815 and 460 Ma for the GHS in Langtang. Regional variations in the composition and thickness of the GHS along the length of the Himalaya are attributed to siliciclastic depocentres centred on Zanskar in northern India, Langtang and Everest in central to western Nepal, which contrast with coeval marine carbonate shelf deposition in the Annapurna region. The protolith lithostratigraphy documented for Langtang provides a coherent framework for interpreting subsequent Cenozoic Himalayan deformation, specifically the homogeneously distributed layer-normal shortening (i.e. flattening) and layer-parallel stretching (i.e. transport-parallel stretching) that characterizes the GHS. Within the context of a single protracted northern Indian marginal sedimentary succession, the distinction between the Lesser, Greater and Tethyan Himalaya is structural rather than lithostratigraphic in origin.

Seasonal Variation in Fluoride Content in Groundwaters of Langtang Area, Northcentral Nigeria

Abstract Thirty groundwater samples were collected at the peak of the rainy season and analysed for fluoride and other cations and anions in drinking water sources of Langtang area. For comparative purposes, thirty seven groundwater samples were collected in the dry season. The aim of the study was to determine variation in fluoride content with respect to the seasons. Fluoride in water was determined by the Ion Selective Electrode (ISE) and the cations by the Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The anion (sulphate) was determined by Multi – Ion Colorimeter, bicarbonate and chloride by titration method. In addition fluorine content in aquifer materials from a borehole section were determined by Fusion method. The two seasons show variation in content of fluoride in groundwater. Fluoride content in groundwater is higher in the dry season ranging from 0.13 – 10.3 mg/l compared to the 0.06 – 4.60 mg/l values in the rainy season. Content of fluorine (0.01 wt %) in the aquifer materials (sands) is low from depth of 0 to 7.95 m. However, fluorine content increases with depth, from 7.95 to 10.60 m with concentration of 0.04 wt %, 0.05 wt % from 10.60 to 13.25m, and 0.07 wt % from 13.25 to 15.70 m, the content of fluorine however, decreased at depth 15.70 to18.55m with concentration of 0.02 wt % even with fluorite mineral in the aquifer material at this depth. Dilution of fluoride ion as a result of rain input which recharges the aquifer may be the main reason for lower values recorded in the rainy season. Over fifty and sixty percent of waters in both dry and rainy season have fluoride concentration above the WHO upper limit of 1.5 mg/l. Consumption of these elevated values of fluoride in groundwater of the study area, clearly manifests as symptoms of dental fluorosis.

Petrological constraints on the tectonic setting of the Kathmandu Nappe in the Langtang–Gosainkund–Helambu regions, Central Nepal Himalaya

AbstractThe Gosainkund–Helambu region in central Nepal occupies a key area for the development of Himalayan kinematic models, connecting the well‐investigated Langtang area to the north with the Kathmandu Nappe (KN), whose interpretation is still debated, to the south. In order to understand the structural and metamorphic architecture of the Greater Himalayan Sequence (GHS) in this region, a detailed petrological study was performed, focusing on selected metapelite samples from both the Gosainkund–Helambu and Langtang transects. The structurally lowest sample investigated belongs to the Lesser Himalayan Sequence; its metamorphic evolution is characterized by a narrow hairpin P–T path with peak P–T conditions of 595 ± 25 °C, 7.5 ± 1 kbar. All of the other samples here investigated belong to the GHS. Along the Langtang section, two tectono‐metamorphic units have been distinguished within the GHS: the Lower Greater Himalayan Sequence (L‐GHS), characterized by peak P–T conditions at 728 ± 11 °C, 10 ± 0.5 kbar (corresponding to a T/depth ratio of 22 ± 1 °C km−1), and the structurally higher Upper Greater Himalayan Sequence, with peak metamorphic conditions at 780 ± 20 °C, 7.8 ± 0.8 kbar (corresponding to a T/depth ratio of 31 ± 4 °C km−1). This confirms the existence of a main tectono‐metamorphic discontinuity within the GHS, as previously suggested by other authors. The results of petrological modelling of the metapelites from the Gosainkund–Helambu section show that this region is entirely comprised within a sub‐horizontal and thin L‐GHS unit: the estimated peak metamorphic conditions of 734 ± 19 °C, 10 ± 0.8 kbar correspond to a uniform T/depth ratio of 23 ± 3 °C km−1. The metamorphic discontinuity identified along the Langtang transect and dividing the GHS in two tectono‐metamorphic units is located at a structural level too high to be intersected along the Gosainkund–Helambu section. Our results have significant implications for the interpretation of the KN and provide a contribution to the more general discussion of the Himalayan kinematic models. We demonstrate that the structurally lower unit of the KN (known as Sheopuri Gneiss) can be correlated with the L‐GHS unit; this result strongly supports those models that correlate the KN to the Tethyan Sedimentary Sequence and that suggest the merging of the South Tibetan Detachment System and the Main Central Thrust on the northern side of the KN. Moreover we speculate that, in this sector of the Himalayan chain, the most appropriate kinematic model able to explain the observed tectono‐metamorphic architecture of the GHS is the duplexing model, or hybrid models which combine the duplexing model with another end‐member model.

Hydrogeochemical appraisal of fluoride in groundwater of Langtang area, Plateau State, Nigeria

Consumption of high fluoride in groundwater of Langtang area, manifest in the inhabitants of the area in form of dental fluorosis and skeletal fluorosis in older group. The aim of this study was to appraise the hydrogeochemistry of fluoride in the groundwaters of Langtang area. Thirty seven surface and groundwater samples and nine rock samples were collected in Langtang area for geochemical analysis. The Inductively Coupled Plasma Emission Spectrometry (ICPOES) was used to detect cations. The anions (Cl - , SO 4 = and Br - ) were determine by Ion Chromatography method. Fluoride was determined by the Specific Ion Electrode and bicarbonate was determined by titration. Major oxides, trace elements and rare earth elements for the rock samples were determined by the XRF method and fluorine by the Fusion method. Polished thin sections for rocks were prepared and studied. Geochemical results from analysis of the samples (rock and water) show that four major rock units make up the geology of the area; coarse porphyritic biotite granite, migmatite, rhyolite and riebeckite granites, the minor ones are pegmatite, trachyte, aplite and fine to medium grained biotite granites. The rhyolite, the riebeckite granites and trachyte have the highest level of fluorine content in the area (1,470, 1000, 900 and 800 ppm) respectively. The fluorine mineral (Fluorite) crystallized in the late stage of the magma as replacement of Fe/Mg mineral probably hornblende or biotite. Fluorine is leached into the groundwater from the rhyolite under the slightly alkaline (Ca-Mg-HCO 3 evolving Na-HCO 3 ) water in the area. The two major groundwater types (Ca-Mg-HCO 3 and Na-HCO 3 ) in the area have good relationship with content of fluoride in water. Although, the riebeckite granites have high fluorine content, contribution of fluoride from them is towards the southern portion of the map, owing to the groundwater flow direction. The different water sources in the area do not show variation in content of fluoride in water. However, groundwater barriers (dykes) may be responsible for some area having low fluoride (<1.5 mg/l) content. The consumption of high content of fluoride in the area has resulted in severe dental fluorosis in both children and youths and bowing of legs ( Genu Valgum ) in children with no discrimination between the sexes. Keywords: Fluoride, Fluorite, Fluorine, Fluorosis, Riebeckite Granite, Groundwater

Two times lowering of lake water at around 48 and 38 ka, caused by possible earthquakes, recorded in the Paleo-Kathmandu lake, central Nepal Himalaya

Sedimentary facies and micro-fossil analyses, and AMS14C dating were performed in order to reveal the water-level fall events and draining process of the lake (Paleo-Kathmandu Lake) that existed in the past in the Central Nepal Himalaya. The sedimentary facies change from the lacustrine Kalimati Formation to the deltaic Sunakothi Formation in the southern and central Kathmandu basin, and the abrupt and prominent increase of phytoliths Bambusoideae and Pediastrum, and contemporaneous decrease of sponge spicule and charcoal grains around 48 and 38 ka support the lowering of water level at these times. According to the pollen analysis, both events occurred under rather warm and wet climate, thus supporting that they were triggered by tectonic cause and not by climate change. The first event might be linked to a possible occurrence of a large earthquake with an epicenter in the vicinity of the Paleo-Kathmandu Lake. The occurrence of a mega landslide in Langtang area close to the north of the Kathmandu Valley producing pseudotachylite dated at 51 ± 13 ka could be linked to this earthquake. Finally, the water was completely drained out from the remnant lake at the central part of the Kathmandu basin by ca.12 ka.

Assessment of Forest Carbon Stocks in the Himalayas: Does Legal Protection Matter?

Although protected areas are central to global biodiversity conservation, most land lies within unprotected areas. In the developing world forest habitats have received increased attention for their potential as carbon sinks in a climate change perspective, and only few of these forests fall within protected areas. This study assesses how various management regimes, within and outside legal protection, influence forest carbon stocks in temperate broad-leaved forests in the Langtang area of Nepal. Woody biomass stocks, as well as soil organic carbon, were estimated using allometric relationships and converted into carbon estimates by standard equations. Regardless of the high similarity in species composition between the two forest management types, trees in the protected forest (PF) inside Langtang National Park were significantly taller and relatively larger than those in the government forest (GF) outside at Bhalche. Also, above-ground (AG) biomass, and hence AG carbon stocks, and soil organic carbon, were higher in the comparatively healthier PF; the total carbon stock was 284.5 ton/ha in the PF, compared to 167.0 ton/ha in the GF. Similarly, the total carbon pool was slightly greater at higher elevation under both management regimes. It was, however, much lower on the southern slope inside the protected forest because people extracted forest biomass, despite the legal protection, this area being close to settlements. Hence, the extent of biomass extraction determines the forest carbon storage capacity. Notably, it is not the legal protection per se, but rather its level of implementation on the ground that determines its success in protecting natural resources. This is in turn contingent on creating alternative livelihood options for communities relying directly on natural resource extraction.

Overview of fluoride distribution in major aquifer units of northern Nigeria

Symptoms of dental fluorosis such as mottled teeth are common among adults, youth and children in several rural communities in northern Nigeria. This has inspired the Authors to investigate the concentration of fluoride in the natural water systems of the major aquifer units (Basement, Sedimentary, Volcanic and Younger Granites) in some parts of northern Nigeria and to delineate areas of high risk of dental fluorosis, crippling skeletal fluorosis and dental caries. Six hundred and twenty seven analytical values for water were obtained from the literature and from analysis of samples from the major aquifer units of northern Nigeria: Basement-232, Sedimentary-328, Younger Granites-38 and Volcanic-28. Fluoride concentrations range from 0.03 to 10.30 mg/L in the Basement Aquifer; 0.00 to 5.00 mg/L in the Sedimentary Aquifer; 0.00 to 0.89 mg/L in the Younger Granites Aquifer; and 0.00 to 0.78 mg/L in the Volcanic Aquifer. A background value of 1.0 mg/L for fluoride concentration for northern Nigeria has been determined in this study. Areas identified with high fluoride in their waters above the World Health Organisation (WHO) recommended maximum permissible level in drinking water of 1.5 mg/L are: Dzuma, Dilchidima, Ngalbi, Udin, Kaltungo Biliri, Shongwom, Dass in the the northeast basement aquifers; Maiduguri, Mafa, Mobbar, Ngala, Logomani, Gombe in the northeast sedimentary aquifers: Langtang, Dorong, Furzi in the north-central basement aquifers and Pakoro in the northcentral sedimentary aquifers: Shawo and Barkin Lamba in the northwest basement aquifers. No anomalously high values of fluoride were recorded in the northwest sedimentary aquifers. All waters sampled in the Younger Granites and the Volcanic Aquifers have fluoride contents lower than the WHO recommended maximum permissible level in drinking water of 1.5 mg/L; and over ninety percent of the waters have fluoride concentration below the 0.5 mg/L recommended by WHO for the prevention of dental caries. Positive correlation between dental fluorosis and high fluoride water consumption has been established in all the areas with high fluoride in their waters. Positive correlation has also been established between genu valgum (bowing of legs) and consumption of high fluo-ride waters in Langtang Area. These data have been used to delineate areas of the Younger Granites Province and the Volcanic Province where inhabitants are at high risk of having dental caries.

Occurrence of fluoride in the drinking waters of Langtang area, north central Nigeria

The aim of the study is to assess the occurrence of fluoride in the drinking water sources of Langtang area. Out of the thirty seven water samples collected from drinking water sources (hand dug wells, boreholes, streams and a spring) and analysed. Results revealed that except for fluoride, all other parameters are within the World Health Organisation recommended limits for water consumption. Fluoride in the waters ranges from 0.12 - 10.30 mg/l with a mean of 2.42 mg/l. low levels of fluoride are recorded in the stream samples. However, no clear variations in fluoride content have been observed in both the borehole samples and those from the hand dug wells. Negative correlation exhibited between fluoride and sulphate, fluoride and Phosphate and the poor correlation between fluoride and nitrate, fluoride and chloride rules out the possibility of anthropogenic source of the fluoride in the waters. Positive correlation between lithium and magnesium, and poor but positive correlation between fluoride and lithium indicate that micas within the host rock and the pegmatite may be responsible for leaching fluoride into the waters. Two of the major water types; Ca + Mg-HCO3 and the Na + K-HCO3 water type obtain in the area have good association with fluoride content. Consumption of high fluoride waters clearly manifests in the inhabitant of the area in form of dental fluorosis and bowing of legs especially in children between the ages 7 - 11 years.

Isotopic study of the Himalayan metamorphic rocks in the far-eastern Nepal

Previous studies have documented that Sr-Nd and U-Pb zircon isotopic compositions are different between the Lesser Himalayan and the Higher Himalayan metamorphic rocks in Nepal, India, and Pakistan (Parrish and Hodges 1996, Ahmad et al. 2000). However, not much attention was paid to the metamorphic rocks of Main Central Thrust (MCT) zone. We report the result of Sr-Nd isotopic studies in the Higher Himalayan zone, the Lesser Himalayan zone and the MCT zone in far-eastern Nepal. Far-eastern Nepal (Kangchenjunga-Taplejung-Ilam region) comprises three distinct tectonic units: the Higher Himalaya, the Lesser Himalaya and the Sub-Himalaya (Shelling and Arita 1991). Each of these tectonic units is a fault-bound tectonic package. The Higher Himalayan metamorphic rocks consist of mediumto high-grade paragneisses and orthogneisses. The Lesser Himalayan metamorphic rocks comprise primarily metasandstones with intercalations of phyllites and meta-quarzites. The Ilam Nappe is composed of the Higher Himalayan metamorphic rocks. It is a geologically siginificant unit in fareastern Nepal. The Ilam Nappe with no overlying the Tethyan sedimentary rocks has been thrust over the Lesser Himalayan thrust package along the MCT zone up to near the Sub-Himalaya zone in the south. The MCT zone is a ductile-brittle zone with a thickness of less than 1 km to several km. The upper boundary of the MCT zone is known as the Upper MCT (UMCT) and the lower one as the Lower MCT (LMCT). The lithology of the MCT zone is characterized by mylonitic augen gneiss, biotite-muscovitechlorite phyllite with S-shaped garnet and graphitic phyllite. Compositions and zoning patterns of garnets can be discriminated between the MCT zone and the Higher Himalaya. Information on the tectonic disposition prior to the Himalayan orogeny of the geologic units juxtaposed by the MCT is important for understanding the crustal shortening and changes of thermal structure due to the MCT activity. In general, the Higher Himalayan sequence has been considered to be Indian basement in origin, and the Lesser Himalayan sequence has been deposited on the northern margin of the Indian continent in the Precambrian times. However, the Higher Himalayan sequence in the Langtang area, central Nepal yields zircon U-Pb ages of 0.8 to 1.0 Ga, implying a sedimentary provenance of the Late Proterozoic. On the other hand, the Lesser Himalayan sequence contains 1.8 to 2.6 Ga zircons. Therefore, it was proposed that the Higher Himalayan sequence is metasedimentary rocks that were originally deposited north of continental margin than the Lesser Himalayan sequence (Parrish and Hodges 1996). Furthermore, Nd isotope data are useful in distinguishing between Higher Himalayan and Lesser Himalayan zones (Ahmad et al. 2000). These data show that the Nd values for t=1000 Ma in the Higher Himalayan are -10 to -3, whereas these of the Lesser Himalayan are -17 to -7. We have recalculated Nd values at 1000 Ma as this time corresponds to a “Grenville” thermal event in the Himalayas. 17 Samples in the far-eastern Nepal were collected from the Lesser Himalayan, the Higher Himalayan and the MCT zones by the tectonostratigrapic units (Figure 1). The isotopic work presented in this study follows on the structural and petrological studies of Schelling and Arita (1991). In study area the Nd values for t=1000 Ma from rocks of the Higher Himalaya and the Lesser Himalaya are almost within the range of the previous data except for the Tamar Khola Granite. The Nd values for t=1000 Ma obtained are -10 to -2 in the Higher Himalaya and -17 to -15 in the Lesser Himalaya. The Tamar Khola Granite has the Nd value for t=1000 Ma of –11 and the high 147Sm/144Nd. Most samples from the MCT zone have the middle Nd values for t=1000 Ma (-15 to -11) of the samples from Higher Himalaya and Lesser Himalaya (Figure 2a). Similarly, the 87Sr/86Sr values obtained from the MCT zone show the values between those of Higher Himalayan and Lesser Himalayan zones although a few rocks units of Lesser Himalaya have very high 87Sr/86Sr values (Figure 2b). These data may serve to strengthen the opinion that the Higher Himalayan sequence is not Indian basement in origin. Further, these data may suggest that the rocks of the MCT zone fill a gap between the Higher and Lesser Himalayan sequence although Sm-Nd isotopic signiture from them indicate that they had different sediment sources area. Finally, both the Higher and the Lesser Himalayan sequence, including the rocks of the MCT zone between them, may represent thick clastic successions deposited on the north of the thinned continental margin of the Indian basement.

Kinematic history of the Main Central Thrust zone in the Langtang area, Nepal

This paper describes for the first time evidence for a northeastward brittle extensional movement of the Main Central Thrust (MCT) zone overprinting the southward ductile thrust movement. The MCT zone is the major tectonic boundary between the Lesser Himalayan metasedimentary sequence (LHS) and Higher Himalayan crystalline sequence (HHS) and contributes to the kinematic and tectonic evidence of continent–continent collision in the Neogene. The Langtang area, 50 km north of Kathmandu, is a matter of interest in considering the movement of the Kathmandu Nappe because the general trend of foliation of the HHS and the underlying MCT zone is turned from WNW–ESE to N–S or NNE–SSW. The major tectono-lithostratigraphic units of the MCT zone in the study area are divided into three: the lower and middle units included in the LHS and the upper unit even included in the HHS. Characteristic mesoscopic quartz lenses are developed in the schists of the Lower unit forming asymmetric boudins. This asymmetry indicates an extensional (top-to-the-NE) shear sense. However, a thrust sense of top-to-the-SW is also preserved in microscopic ductile shear bands and mica fish. The extensional shear movement in the Lower unit took place after the major thrust movement in the MCT zone as a negative inversion. The Middle unit contains Ulleri-type augen gneiss (Syabru Bensi augen gneiss) which is widely distributed in the MCT zone in the other parts of the Nepalese Himalaya. Asymmetric clast-tails (or clast-pressure shadows) and asymmetric boudins observed in the Syabru Bensi augen gneiss give a dextral-thrust oblique sense of shear. This dextral component is regarded as movement of a N–S-trending lateral ramp during the overthrusting of the Kathmandu Nappe. The Upper unit above the MCT is commonly made up of kyanite-bearing medium pressure type amphibolite-facies pelitic gneiss. Asymmetric deformational features such as mica fish and shear bands in the pelitic gneisses commonly show a thrust (top-to-the-W) sense of movement. After the emplacement of the Kathmandu Nappe (∼9–6 Ma), brittle extensional shear occurred only in the crystalline schists of the Lower unit presumably associated with layer-parallel slip. This extensional movement in the Lower unit is probably caused by the change in strike of foliations, e.g., from a general trend of E–W in the other areas to N–S as seen in the study area. This is because N–S contraction during continued continent–continent collision produced E–W extension normal to the contraction axis (N–S), thus the relative east-directed movement on normal faults took place only in the N–S trending domain of the MCT zone. Another possibility for the extensional movement is squeezing of the upper part of the LHS between the MCT above and an out-of-sequence thrust or the Main Detachment Fault below.

Isotopic constraints on the age and provenance of the Lesser and Greater Himalayan sequences, Nepalese Himalaya

The Main Central thrust of the central Himalaya juxtaposes the Lesser Himalayan sequence (footwall) with the Greater Himalayan sequence (hanging wall), both of which are regarded as components of the northern passive margin of India. Considerable uncertainty surrounds their respective ages and sedimentary derivation. U-Pb and Sm-Nd isotopic studies of samples from the Langtang area, central Nepal, demonstrate important distinctions between the two rock packages. The Greater Himalayan sequence had a sedimentary provenance that included a major source of 0.8–1.0 Ga zircons, implying a Late Proterozoic age. The source of the Precambrian part of the Lesser Himalayan sequence contained 1.87–2.60 Ga zircons, and its depositional age is probably Middle Proterozoic. Nd isotopic characteristics of the two sequences are different: at 21 Ma, the Greater Himalayan rocks had eNd values between −14.6 and −18.5 while their Lesser Himalayan counterparts had values between −21.4 and −25.9, giving rise to major differences in their model ages. The Lesser and Greater Himalayan sequences at Langtang are interpreted as correlative to the lower and upper parts of the Vindhyan Supergroup, currently exposed south of the Gangetic plain in northern India. On the basis of available age data, the exposed hanging wall of the Main Central thrust in central and eastern Nepal contains no Archean-Early Proterozoic basement. If the fault does root into the basement at depth, it must do so farther north than recently published cross sections indicate. This implies a total displacement on the fault that is substantially greater than the 140–210 km required by tectonic overlap in the eastern Himalayas.

An evaluation of the inverted metamorphic gradient at Langtang National Park, Central Nepal Himalaya

Abstract The crystalline core of the Himalayan orogen in the Langtang area of Nepal, located between the Annapurna‐Manaslu region and the Everest region, contains middle to upper amphibolite grade pelitic gneisses and schists. These rocks are intimately associated with the Main Central Thrust (MCT), one of the major compressional structures in the northern Indian plate, which forms a 3.7‐km‐wide zone containing rocks of both footwall and hangingwall affinity. An inverted metamorphic gradient is noticeable from upper footwall through hangingwall rocks, where metamorphic conditions increase from garnet grade near the MCT zone to sillimanite + K‐feldspar grade in the upper hangingwall. Petrographic data distinguish two metamorphic episodes that have affected the area: a high‐pressure, moderate‐temperature episode (M1) and a moderate‐pressure, high‐temperature episode (M2). Comparison with appropriate reaction boundaries suggests that conditions for M1 in the hangingwall were approximately 900–1200 MPa and 425–525°C. Thermobarometric results for 24 samples from the footwall, MCT zone and hangingwall reflect P‐T conditions during the M2 phase of 400–1200 MPa and 490–660° C. The decrease in estimated palaeopressures from footwall to hangingwall approximate a lithostatic gradient of 27 MPa km‐1, with slight fluctuations in the MCT zone reflecting structural discontinuities. In contrast to the palaeopressures, palaeotemperatures are indistinguishable across the entire area sampled. Although field evidence suggests the presence of the inverted palaeothermal gradient well known in the Himalaya, quantitative thermobarometry indicates that temperatures of final equilibration were all within error of each other across 17 km of section. At Langtang, change in pressure is responsible for the presence of the sequence of index minerals through the section. I interpret these data to reflect diachronous attainment of equilibrium temperature conditions in a lithostatic palaeopressure profile after ductile faulting of the sequence.