The basic concept of phytosociology is crucial for the assessment of species composition and dynamic ecological succession of forests supporting ecological services,functions,disturbance,and resilience that lead to th...The basic concept of phytosociology is crucial for the assessment of species composition and dynamic ecological succession of forests supporting ecological services,functions,disturbance,and resilience that lead to the development of integrated areas such as ecological niche modeling and contribute to identifying the valuable bio-indicators which can be used in framing conservation and management planning.B.utilis is one of the most dominant tree species of treeline ecotone in the Himalayan Region.The species is also considered as indicator species for monitoring the past and recent climate change impact.The current study was carried out in the natural populations of B.utilis from the sub-alpine zone of North-western Indian Himalaya.The birch dominated forest harbors a total of 305 plant species comprising Angiosperms(51 families,160 genera and 277 species),Gymnosperms(03 families,05 genera and 07 species)and Pteridophytes(07 families,11 genera and 21 species)with Asteraceae,Ranunculaceae and Rosaceae as dominant family.Birch forests are found dominant in shady moist habitat and North West aspect.Geographical characteristics,anthropogenic and developmental activities affect the population structure of B.utilis and associated species.However,the species has fair regeneration status in the study area.The acidic nature of soil pH and spatial variation in edaphic characteristics may be due to geographical differences,rooting patterns and litter accumulation of below and above-ground vegetation.Biomass estimation of a representative population of B.utilis from each site showed that TAGBD,TCD and TBD were found maximum in ST3(Hamta Pass II site).The CCA analysis determined that environmental variables such as altitude,organic matter,available phosphorous,organic carbon,available nitrogen,and electrical conductivity played a significant role in determining tree species composition and distribution in B.utilis dominated forests.展开更多
Himalayan glaciers are shrinking rapidly,especially after 2000.Glacier shrinkage,however,shows a differential pattern in space and time,emphasizing the need to monitor and assess glacier changes at a larger scale.In t...Himalayan glaciers are shrinking rapidly,especially after 2000.Glacier shrinkage,however,shows a differential pattern in space and time,emphasizing the need to monitor and assess glacier changes at a larger scale.In this study,changes of 48 glaciers situated around the twin peaks of the Nun and Kun mountains in the northwestern Himalaya,hereafter referred to as Nun-Kun Group of Glaciers(NKGG),were investigated using Landsat satellite data during 2000-2020.Changes in glacier area,snout position,Equilibrium Line Altitude(ELA),surface thickness and glacier velocity were assessed using remote sensing data supplemented by field observations.The study revealed that the NKGG glaciers have experienced a recession of 4.5%±3.4%and their snouts have retreated at the rate of 6.4±1.6 m·a^(-1).Additionally,there was a 41%increase observed in the debris cover area during the observation period.Using the geodetic approach,an average glacier elevation change of-1.4±0.4 m·a^(-1)was observed between 2000 and 2012.The observed mass loss of the NKGG has resulted in the deceleration of glacier velocity from 27.0±3.7 m·a^(-1)in 2000 to 21.2±2.2 m·a^(-1)in 2020.The ELA has shifted upwards by 83.0±22 m during the period.Glacier morphological and topographic factors showed a strong influence on glacier recession.Furthermore,a higher recession of 12.9%±3.2%was observed in small glaciers,compared to 2.7%±3.1%in larger glaciers.The debris-covered glaciers showed lower shrinkage(2.8%±1.1%)compared to the clean glaciers(9.3%±5%).The glacier depletion recorded in the NKGG during the last two decades,if continued,would severely diminish glacial volume and capacity to store water,thus jeopardizing the sustainability of water resources in the basin.展开更多
The increasing demand for water and energy resources has led to widespread dam construction,particularly in ecologically sensitive regions like the Himalayan Range.This study focuses on the Uttarakhand state in the We...The increasing demand for water and energy resources has led to widespread dam construction,particularly in ecologically sensitive regions like the Himalayan Range.This study focuses on the Uttarakhand state in the Western Himalayas,where hydroelectric projects(HEPs)have significantly altered river flow regimes.The research investigates the impact of flow alterations on the composition and structure of riparian vegetation in the Garhwal Himalayas,specifically analysing four rivers regulated by hydroelectric projects.Utilizing the paired-reach comparison method,control(undisturbed),diverted(downstream of barrage/dam),and altered flow conditions(downstream of water outlet)were examined.The research reveals diverse and unique riparian ecosystems,with 89 genera and 113 taxa identified,showcasing the dominance of families like Asteraceae and Lamiaceae.The study unveils the structural importance of key species such as Berberis asiatica and Artemisia nilagirica.The density,diversity,and richness of shrub and herb species vary significantly across flow conditions.Notably,altered flow conditions demonstrate resilience in vegetation structure,while diverted conditions exhibit decreased species richness and density.The study emphasizes the importance of nuanced environmental flow management for mitigating adverse effects on riparian biodiversity in the fragile Himalayan region.These findings contribute to the global discourse on dam impacts and riparian ecology,shedding light on the complexities of this dynamic relationship in a vulnerable ecosystem.展开更多
The Eastern Himalayas are renowned for their high plant diversity.To understand how this modern botanical richness formed,it is critical to investigate past plant biodiversity preserved as fossils throughout the easte...The Eastern Himalayas are renowned for their high plant diversity.To understand how this modern botanical richness formed,it is critical to investigate past plant biodiversity preserved as fossils throughout the eastern Himalayan Siwalik succession(middle Miocene-early Pleistocene).Here,we present a summary of plant diversity records that document Neogene floristic and climate changes.We do this by compiling published records of megafossil plant remains,because these offer better spatial and temporal resolution than do palynological records.Analyses of the Siwalik floral assemblages based on the distribution of the nearest living relative taxa suggest that a tropical wet evergreen forest was growing in a warm humid monsoonal climate at the deposition time.This qualitative interpretation is also corroborated by published CLAMP(Climate Leaf Analysis Multivariate Program) analyses.Here,we also reconstruct the climate by applying a new common proxy WorldClim2 calibration.This allows the detection of subtle climate differences between floral assemblages free of artefacts introduced by using different methodologies and climate calibrations.An analysis of the Siwalik floras indicates that there was a gradual change in floral composition.The lower Siwalik assemblages provide evidence of a predominance of evergreen elements.An increase in deciduous elements in the floral composition is noticed towards the close of the middle Siwalik and the beginning of the upper Siwalik formation.This change reflects a climatic difference between Miocene and Plio-Pleistocene times.This review helps us to understand under what paleoenvironmental conditions plant diversity occurred and evolved in the eastern Himalayas throughout the Cenozoic.展开更多
While the need for understanding the effects of topographical factors on forest structure and function is well recognized,comprehensive studies are scarce.This study evaluates the effect of slope aspect and slope posi...While the need for understanding the effects of topographical factors on forest structure and function is well recognized,comprehensive studies are scarce.This study evaluates the effect of slope aspect and slope position on water relations and forest attributes across six forest types occurring between 400 m and 2600 m altitude in the Central Himalaya(27°-38°N).We found that predawn tree water potential and soil water potential were generally higher on moist north slope aspect(-0.78±0.05 MPa and-3.34±0.18 MPa,respectively)than dry south slope aspect(-0.82±0.18 MPa and-3.77±0.18 MPa,respectively).Across six different forests,these values were higher at hill base(-0.71±0.06 MPa and-2.77±0.19 MPa,tree predawn water potential and soil water potential,respectively)than other topographical positions.The favorable effect of north aspect and hill base was also observed in maintaining soil water and tree water potential during the dry season.Vegetation attributes,such as species richness,unique species and plant density were also generally higher on north slope and hill base than southern aspect and lowest at hill top.Across forest types,the hill base provided shelter to 46 unique species,compared to 16-18 at the other positions,thus emphasizing its importance as refugia for species to survive climate change induced perturbations.The favorable conditions of hill base position not only contribute to increase in alpha diversity,but also to extended species distributional range.展开更多
The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the ...The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the active age is earlier than the peak ages of the Kerguelen mantle plume.This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume.The intrusion in the Dingri area contains diabases and monzonites.The zircon age of diabase is 123±1 Ma,and that of monzonite is 117±1 Ma.Geochemistry and Sr-Nd isotopic analyses show that the mafic-intermediate dikes were formed in an intraplate extensional environment.The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust,with both magmatic evolutions being contaminated by crustal materials.These characteristics are similar to those of the Rajmahal-Sylhet basalt,a typical Kerguelen mantle plume product.The discovery of the Dingri mafic-intermediate dikes of the central TH suggests that the TH and Rajmahal-Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.展开更多
The Garhwal Himalaya is among the major repositories of immensely valuable wild edible plants and provides food security to the local population.Among the valuable plant species that grow in this region,Paeonia emodi(...The Garhwal Himalaya is among the major repositories of immensely valuable wild edible plants and provides food security to the local population.Among the valuable plant species that grow in this region,Paeonia emodi(family Paeoniaceae)is an important wild edible species that found in temperate regions with an altitude range between 1800 and 2800 m.The species is facing a severe threat to its sustainability due to overharvesting,habitat disturbances,and a lack of effort regarding conservation.For the first time,this study investigated anthropogenic pressure,population decline perceptions in the natural habitat,and vulnerability assessment of P.emodi under selected study sites(n=23 villages).A semi structured questionnaire was used to interview approximately 45%of the local inhabitants,including herbal practitioners(Vaidhyas or Dais)of each village.On the basis of demographic characteristics,the perceptions and responses of 464 local people were documented regarding potential causes of deterioration and feasible options for sustainable utilization.Using the weight survey method,we estimated the actual amount of collection based on personal interaction and direct observation.In order to determine the threats status,a rapid vulnerability assessment(RVA)was performed and were used based on the current exploitation and usage.The present study revealed that leaf(100%)was the most frequently harvested part,followed by stem(95.65%),seed(26.09%),root(21.74%)and flower(13.04%).The village Triyuginarayan and Pothivasa recorded the highest collection scores while the purpose of the collection was mostly edible(100%),medicinal(100%),and least commercial(8.70%).According to the literature review and the present survey,the RVA(total=21)is categorized as category II(intermediate side of the RVA index),indicating a degree of vulnerability.The study revealed that P.emodi faces extinction in the Garhwal Himalayas.Growing this species through agro-production techniques may alleviate the pressure on the existing population as a result of the availability of raw materials for commercial and household uses.These findings will provide an effective framework for conservation and management decisions and plans.展开更多
Glacier shrinkage is a globally occurring phenomena.High-resolution change detection based on frequent mapping and monitoring of high-altitude glaciers is necessary to precisely evaluate future water availability and ...Glacier shrinkage is a globally occurring phenomena.High-resolution change detection based on frequent mapping and monitoring of high-altitude glaciers is necessary to precisely evaluate future water availability and to understand glacier evolution under different climatic scenarios in the Hindukush-Karakoram-Himalayan(HKH)region.This also holds true for the Bhaga basin of the western Himalaya.This study investigates glacier and glacier lake changes in the Bhaga basin,over the last five decades based on satellite imagery including Corona KH4(1971),Landsat 7 Enhanced Thematic Mapper Plus(ETM+;2000),Linear Imaging Self-Scanning Sensor(LISS Ⅳ;2013),and Sentinel 2(2020).Regional temperature and precipitation trends were evaluated from gridded climatic datasets(1900–2020).In the Bhaga basin 306 glaciers(>0.2 km^(2))were mapped with a total area of 360.3±4.0 km^(2),of which 55.7±0.6 km^(2)was covered with debris in 2013.The total glacier covered area decreased by∼8.2±1.5%(0.16±0.03%yr-1)during the entire observation period 1971–2020,with noticeable heterogeneity between tributary watersheds.In the past two decades(2000–2020),the deglaciation rate has increased significantly(0.25%yr-1)compared to the previous decades(1971–2000;0.12%yr-1).Glacier lake area increased by 0.6±0.1 km^(2)(0.012 km^(2)yr-1)between 1971 and 2020.The NCEP/NCAR climatic data reveals an increase of 0.63℃in temperature and a decrease of 6.39 mm in precipitation for the period 1948–2018.In comparison,APHRODITE data shows an increasing trend in temperature of 1.14℃between 1961 and 2015 and decreasing trend in precipitation of 31 mm between 1951 and 2007.Both NCEP/NCAR and APHRODITE data reveal significant temperature increase and precipitation decrease since the 1990s,which have probably augmented ice loss in the Bhaga basin during the early 21st century.展开更多
Glacier response patterns at the catchment scale are highly heterogeneous and defined by a complex interplay of various dynamics and surface factors.Previous studies have explained heterogeneous responses in qualitati...Glacier response patterns at the catchment scale are highly heterogeneous and defined by a complex interplay of various dynamics and surface factors.Previous studies have explained heterogeneous responses in qualitative ways but quantitative assessment is lacking yet where an intrazone homogeneous climate assumption can be valid.Hence,in the current study,the reason for heterogeneous mass balance has been explained in quantitative methods using a multiple linear regression model in the Sikkim Himalayan region.At first,the topographical parameters are selected from previously published studies,then the most significant topographical and geomorphological parameters are selected with backward stepwise subset selection methods.Finally,the contributions of selected parameters are calculated by least square methods.The results show that,the magnitude of mass balance lies between-0.003±0.24 to-1.029±0.24 m.w.e.a^(-1) between 2000 and 2020 in the Sikkim Himalaya region.Also,the study shows that,out of the terminus type of the glacier,glacier area,debris cover,ice-mixed debris,slope,aspect,mean elevation,and snout elevation of the glaciers,only the terminus type and mean elevation of the glacier are significantly altering the glacier mass balance in the Sikkim Himalayan region.Mathematically,the mass loss is approximately 0.40 m.w.e.a^(-1) higher in the lake-terminating glaciers compared to the land-terminating glaciers in the same elevation zone.On the other hand,a thousand meters mean elevation drop is associated with 0.179 m.w.e.a-1of mass loss despite the terminus type of the glaciers.In the current study,the model using the terminus type of the glaciers and the mean elevation of the glaciers explains 76% of fluctuation of mass balance in the Sikkim Himalayan region.展开更多
Leishmaniasis is a vector-borne parasitic disease affecting millions of people worldwide.However,in the last decade,the number of cases has been reduced from well-documented endemic parts,but sporadic cases have been ...Leishmaniasis is a vector-borne parasitic disease affecting millions of people worldwide.However,in the last decade,the number of cases has been reduced from well-documented endemic parts,but sporadic cases have been reported widely from various non-endemic areas,especially from the southern Himalayan zone.This raises concerns about the emergence of new ecological niches.This warrants a critical evaluation of key factors causing this rapid spread and possibly indigenous transmission.This mini-review article is aimed to briefly address the parasite,the vector,and the environmental aspects in the transmission of leishmaniasis in these new foci against a background of worldwide endemic leishmaniasis with a special focus on the southern Himalayan zone.As the lack of knowledge about the causative parasites,vectors,reservoir hosts,atypical presentations,and their management make the problem serious and may lead to the emergence of public health issues.The present works also reviewed the existing information regarding clinical variations,diagnostic methods,treatment,its outcome,and ignite for further research in these aspects of the disease.展开更多
The fragmented pattern and the rapidly declining preservation of older glacial features/evidences limits the precision,with which glacial chronologies can be established.The challenge is exacerbated by the scarcity of...The fragmented pattern and the rapidly declining preservation of older glacial features/evidences limits the precision,with which glacial chronologies can be established.The challenge is exacerbated by the scarcity of datable material and limitations of dating methods.Nevertheless,the preserved glacial landforms have been fairly utilized to establish glacial chronologies from different sectors of the Indian Himalayas.The existing Himalayan glacial chrono-stratigraphies have revealed that in a single valley,past glacial advances rarely surpass four stages.Thus,local and regional glacial chronologies must be synthesized to understand glacial dynamics and potential forcing factors.This research presents an overview of glacier responses to climate variations revealed by glacial chrono-stratigraphies in the western Indian Himalayan region over the Quaternary(late).The synthesis demonstrated that,although the glacial advances were sporadic,glaciers in western Himalayas generally advanced during the Marine isotope stage(MIS)-3/4,MIS-2,late glacial,Younger Dryas(YD)and Holocene periods.The Holocene has witnessed multiple glacial advances and the scatter is significant.While previous glacial research revealed that Himalayan glaciers were out of phase with the global last glacial maximum(gLGM),weak Indian Summer Monsoon(ISM)has been implicated(ISM was reduced by roughly 20%).Recent research,however,has shown that gLGM glaciation responded to the global cooling associated with the enhanced mid-latitude westerlies(MLW).Further,the magnitude of gLGM glacier advance varied along and across the Himalayas particularly the transitional valleys located between the ISM and MLW influence.It is also evident that both the ISM and MLW have governed the late Quaternary glacial advances in the western Himalayan region.However,the responses of glaciers to ISM changes are more prominent.The insights gained from this synthesis will help us understand the dynamics of glacier response to climate change,which will be valuable for future climate modelling.展开更多
Sikkim Himalaya hosts critical water resources such as glacial,rain,and snow-fed springs and lakes.Climate change is adversely affecting these resources in various ways,and elevation-dependent warming is prominent amo...Sikkim Himalaya hosts critical water resources such as glacial,rain,and snow-fed springs and lakes.Climate change is adversely affecting these resources in various ways,and elevation-dependent warming is prominent among them.This study is a discussion of the elevation-dependent warming(EDW),snowfall shift,and precipitation variability over Sikkim Himalaya using a high-resolution ERA5-land dataset.Furthermore,the findings show that the Sikkim Himalaya region is experiencing a warming trend from south to north.The majority of the Sikkim Himalayan region shows a declining trend in snowfall.A positive advancement in snowfall trend(at a rate of 1 mm per decade)has been noticed above 4500 meters.The S/P ratio indicates a shift in snowfall patterns,moving from lower elevations to much higher regions.This suggests that snowfall has also transitioned from Lachung and Lachen(3600 m)to higher elevated areas.Moreover,the seasonal shifting of snowfall in the recent decade is seen from January-March(JFM)to February-April(FMA).Subsequently,the preceding 21 years are being marked by a significant spatiotemporal change in temperature,precipitation,and snowfall.The potent negative correlation coefficient between temperature and snowfall(–0.9),temperature and S/P ratio(–0.5)suggested the changing nature of snowfall from solid to liquid,which further resulted in increased lower elevation precipitation.The entire Sikkim region is transitioning from a cold-dry to a warm-wet weather pattern.In the climate change scenario,a drop in the S/P ratio with altitude will continue to explain the rise in temperature over mountainous regions.展开更多
The current article is an opinion on the sensitivity of high mountain regions which are the most fragile,sensitive and vulnerable to ongoing climate change.Its impacts are especially severe on the high mountain commun...The current article is an opinion on the sensitivity of high mountain regions which are the most fragile,sensitive and vulnerable to ongoing climate change.Its impacts are especially severe on the high mountain communities owing to their weak socio-economic profile,limited livelihood resources and agricultural land.The melting of glaciers and changes in the snow cover under the climate change scenario is leading to the scarcity of freshwater supplies,affecting both local and downstream communities.Changes in the precipitation patterns have been suggested to cause droughts,impact restricted agriculture,and limit the availability of water for domestic use.Additionally,the high mountain areas contain distinct flora and fauna,and climate change is not just altering them,but also has resulted in biodiversity loss as species are unable to adapt to the changing climate.Because of its higher altitudes and semi-arid to arid climate,the consequences of climate change are more evident in the higher Himalayas.Climate change is affecting the availability of key resources,such as freshwater and agriculture and pasture lands,resulting in food and water insecurity and their reliance on imports from other regions.As a result,high mountain communities in the Himalayas are progressively shifting to higher glacier valleys in search of suitable cultivable land with adequate irrigation.People are engaging in agro-pastoral activities around thermokarst lakes(Oasis)atop rock glaciers as part of this endeavour.Such actions underscore the crucial role of rock glaciers in dealing with and adjusting to the consequences of climate change.Despite its relevance,rock glacier research in the Himalayan region is still in its infancy.The purpose of this work is to emphasise the significance of these major climate-resilient water resources,as well as the methodology that must be adopted for their systematic and compressive investigations.展开更多
The Eastern Sikkim area forming a part of the Lesser Himalaya is located between 27°10′～27°30′N latitudes and 88°25′～88°40′E longitudes (750km 2). The previous workers agreed that a domal str...The Eastern Sikkim area forming a part of the Lesser Himalaya is located between 27°10′～27°30′N latitudes and 88°25′～88°40′E longitudes (750km 2). The previous workers agreed that a domal structure is present in Sikkim which is constituted by low to high grade metamorphic rocks characterised by inverted metamorphism. The rocks were repeatedly deformed and were metamorphosed at about 550 to 770℃ (550 to 750MPa). Geologically, the oldest rocks of Eastern Sikkim are represented by Darjeeling Formation showing medium to high grade metamorphism. It is followed by low grade Daling Formation which is characterised by tectonic wedges of Lingtse gneiss. The potassic syenite intrusive i.e. the Sikkim igneous formation is youngest rock type of the area. The Darjeeling Formation associated with amphibolite bands consists of kyanite\|sillimanite, staurolite and garnet zones, while the Daling Formation is characterised by low grade chloritoid and chlorite zones. Lingtse Formation is gneissic in which patches of retrograded and sheared garnet schists are present. Intrusions of potassic syenites (Sikkim Formation) occur in the form of oval and concordant bodies. The F 1, F 2 and F 3 folds are well developed in rocks of Eastern Sikkim area.. The F 1 folds are rootless, tightly isoclinal or reclined and highly obliterated in their attitude. The F 2 folds belong to class IC of Ramsay (1967). Their interlimb angles vary from 20～50 degrees. Intersection lineation due to S 0/S 1 and S 2 surfaces is parallel to the F 2 folds axis. Third generation structures are represented by open to moderately tight and kinked folds. Superimposition of F 3 folds on F 2 folds resulted into type II interference pattern of Ramsay (1967). Structural analysis of these folds have revealed that F 2 folds are non\|cylindrical. The kink or F 3 folds were possibly responsible for the formation of a megakink resembling with the domal structure. The repeatedly deformed rocks of Eastern Sikkim area were folded, faulted, sheared/thrusted during the Himalayan orogeny. The Main Central Thrust (M C T) is actually a ductile shear zone and was subjected to imbrication during later phases of F 2 folding.展开更多
The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone t...The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.展开更多
New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase m...New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.展开更多
The Upper Triassic flysch sediments(Nieru Formation and Langjiexue Group)exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalaya...The Upper Triassic flysch sediments(Nieru Formation and Langjiexue Group)exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen.This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area.The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances.The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust.These rocks have relatively low Chemical Index of Alteration values(with an average of 62)and Index of Compositional Variability values(0.69),indicating that they experienced weak weathering and were mainly derived from a mature source.The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidicintermediate igneous source.Furthermore,hornblende and feldspar experienced decomposition in the provenance,and the sediment became enriched in zircon and monazite during sediment transport.The detrital zircons in the strata feature two main age peaks at 225-275 Ma and 500-600 Ma,nearly continuous Paleoproterozoic to Neoproterozoic ages,and a broad inconspicuous cluster in the Tonian-Stenian(800-1200 Ma).The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300-325 Ma(characteristic of the Lhasa block)and 1150-1200 Ma(characteristic of the Lhasa and West Australia blocks).Therefore,neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata.Newly discovered Permian-Triassic basalt and mafic dikes in the Himalayas could have provided the 225-275 Ma detrital zircons.Therefore,Indian and Himalayan units were the main provenances of the flysch strata.The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous.This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.展开更多
Prevailing dogma asserts that the uplift of Tibet, the onset of the Asian monsoon system and high biodiversity in southern Asia are linked, and that all occurred after 23 million years ago in the Neogene.Here, spannin...Prevailing dogma asserts that the uplift of Tibet, the onset of the Asian monsoon system and high biodiversity in southern Asia are linked, and that all occurred after 23 million years ago in the Neogene.Here, spanning the last 60 million years of Earth history, the geological, climatological and palaeontological evidence for this linkage is reviewed. The principal conclusions are that: 1) A proto-Tibetan highland existed well before the Neogene and that an Andean type topography with surface elevations of at least 4.5 km existed at the start of the Eocene, before final closure of the Tethys Ocean that separated India from Eurasia. 2) The Himalaya were formed not at the start of the India-Eurasia collision, but after much of Tibet had achieved its present elevation. The Himalaya built against a pre-existing proto-Tibetan highland and only projected above the average height of the plateau after approximately 15 Ma. 3)Monsoon climates have existed across southern Asia for the whole of the Cenozoic, and probably for a lot longer, but that they were of the kind generated by seasonal migrations of the Inter-tropical Convergence Zone. 4) The projection of the High Himalaya above the Tibetan Plateau at about 15 Ma coincides with the development of the modern South Asia Monsoon. 5) The East Asia monsoon became established in its present form about the same time as a consequence of topographic changes in northern Tibet and elsewhere in Asia, the loss of moisture sources in the Asian interior and the development of a strong winter Siberian high as global temperatures declined. 6) New radiometric dates of palaeontological finds point to southern Asia's high biodiversity originating in the Paleogene, not the Neogene.展开更多
Geological evidences have indicated large\|scale crustal shortening by thrust faultings in Himalaya , such as MCT and MBT. The thrust faulting near Yarlungzampbo suture was also observed. However, it is still unknown ...Geological evidences have indicated large\|scale crustal shortening by thrust faultings in Himalaya , such as MCT and MBT. The thrust faulting near Yarlungzampbo suture was also observed. However, it is still unknown to what depth those thrust faultings have been going down into the crust or upper mantle . Seismological evidences indicate that the thrust faultings in Himalaya and southern Tibet have extended to a depth of 80 to 100km , and stopped there. The thrust faultings underneath MCT MBT and Yarlungzampbo suture are closely related to the multiple crustal subductions in Himalaya and southern Tibet. It provides important constraints for the collision process between India and Eurasia. The incomplete crustal subductions in this region suggest that the impinging Indian crust is too light to prevent it going further down, and retreat of crustal subduction is required for the continuing northward movement of the Indian plate. The multiple crustal subductions are compatible to the multiple episodes of the geological activities in Himalaya and southern Tibet. At first, the crustal subduction was produced at Yarlungzampbo suture , and stopped at a depth of 80～100km. Then, it migrated to the south, other new crustal subductions would start successively at MCT and MBT respectively. They stopped at a depth of 80 to 100km also. Beside the north\|dipping seismic zones in Himalaya and Yarlungzamp bo suture, another gentle south\|dipping seismic zone,extending from Tangula Shan at the surface to the Moho at Yarlungzampbo suture was also observed. It can be interpreted to be an obduction at Tangula Shan. The multiple incomplete crustal subductions in Himalaya and Yarlungzampbo suture highly imply that the impinging Indian crust has been splitted apart from its upper\|most mantle, which may b e subducted deeper into the Eurasian mantle.展开更多
Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between I...Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between Indian and Asian continents during Cenozoic.Based on geometric and kinematic mapping of the major boundary or regional faults (Dongjug—Mainling(1), Anigiao(2) and Jali(3), Guyu(4) faults in EHS, Ailaoshan—Red River(5), Lancangjiang(6), Gaoligong(7), Binlangjiang(8) and Magok(9) faults in WSY) (see Fig.1), especially on abundant geochronological dating of the mylonitic rocks along these faults, and coupled with magmato\|metamorphic sequences of this region, we try to deal with the temporal and spatial relationships of collisional process to answer questions such as: (1) when did collision start ? (2) is thrusting as a initial and dominant deformation mode to absorb the crustal shortening after suturing, or earlier thrusting usually followed by large\|scale strike\|slip faults? (3) are the two structural patterns coeval at times, or do they occur alternatively during deformation history? (4) are the collisional and associate uplift processes a continuous one or periodic? Insight into such questions is crucial for better understanding of the continental deformation and testing the models available or constraining a new one.展开更多
基金the GBPI Mountain Division-Himalayan Research Fellowship for financial support
文摘The basic concept of phytosociology is crucial for the assessment of species composition and dynamic ecological succession of forests supporting ecological services,functions,disturbance,and resilience that lead to the development of integrated areas such as ecological niche modeling and contribute to identifying the valuable bio-indicators which can be used in framing conservation and management planning.B.utilis is one of the most dominant tree species of treeline ecotone in the Himalayan Region.The species is also considered as indicator species for monitoring the past and recent climate change impact.The current study was carried out in the natural populations of B.utilis from the sub-alpine zone of North-western Indian Himalaya.The birch dominated forest harbors a total of 305 plant species comprising Angiosperms(51 families,160 genera and 277 species),Gymnosperms(03 families,05 genera and 07 species)and Pteridophytes(07 families,11 genera and 21 species)with Asteraceae,Ranunculaceae and Rosaceae as dominant family.Birch forests are found dominant in shady moist habitat and North West aspect.Geographical characteristics,anthropogenic and developmental activities affect the population structure of B.utilis and associated species.However,the species has fair regeneration status in the study area.The acidic nature of soil pH and spatial variation in edaphic characteristics may be due to geographical differences,rooting patterns and litter accumulation of below and above-ground vegetation.Biomass estimation of a representative population of B.utilis from each site showed that TAGBD,TCD and TBD were found maximum in ST3(Hamta Pass II site).The CCA analysis determined that environmental variables such as altitude,organic matter,available phosphorous,organic carbon,available nitrogen,and electrical conductivity played a significant role in determining tree species composition and distribution in B.utilis dominated forests.
基金as part of the Department of Science and Technology (DST), Government of India sponsored research projects titled “Centre of Excellence for Glaciological Research in Western Himalaya”the financial assistance received from the Department under the projects to conduct the research。
文摘Himalayan glaciers are shrinking rapidly,especially after 2000.Glacier shrinkage,however,shows a differential pattern in space and time,emphasizing the need to monitor and assess glacier changes at a larger scale.In this study,changes of 48 glaciers situated around the twin peaks of the Nun and Kun mountains in the northwestern Himalaya,hereafter referred to as Nun-Kun Group of Glaciers(NKGG),were investigated using Landsat satellite data during 2000-2020.Changes in glacier area,snout position,Equilibrium Line Altitude(ELA),surface thickness and glacier velocity were assessed using remote sensing data supplemented by field observations.The study revealed that the NKGG glaciers have experienced a recession of 4.5%±3.4%and their snouts have retreated at the rate of 6.4±1.6 m·a^(-1).Additionally,there was a 41%increase observed in the debris cover area during the observation period.Using the geodetic approach,an average glacier elevation change of-1.4±0.4 m·a^(-1)was observed between 2000 and 2012.The observed mass loss of the NKGG has resulted in the deceleration of glacier velocity from 27.0±3.7 m·a^(-1)in 2000 to 21.2±2.2 m·a^(-1)in 2020.The ELA has shifted upwards by 83.0±22 m during the period.Glacier morphological and topographic factors showed a strong influence on glacier recession.Furthermore,a higher recession of 12.9%±3.2%was observed in small glaciers,compared to 2.7%±3.1%in larger glaciers.The debris-covered glaciers showed lower shrinkage(2.8%±1.1%)compared to the clean glaciers(9.3%±5%).The glacier depletion recorded in the NKGG during the last two decades,if continued,would severely diminish glacial volume and capacity to store water,thus jeopardizing the sustainability of water resources in the basin.
文摘The increasing demand for water and energy resources has led to widespread dam construction,particularly in ecologically sensitive regions like the Himalayan Range.This study focuses on the Uttarakhand state in the Western Himalayas,where hydroelectric projects(HEPs)have significantly altered river flow regimes.The research investigates the impact of flow alterations on the composition and structure of riparian vegetation in the Garhwal Himalayas,specifically analysing four rivers regulated by hydroelectric projects.Utilizing the paired-reach comparison method,control(undisturbed),diverted(downstream of barrage/dam),and altered flow conditions(downstream of water outlet)were examined.The research reveals diverse and unique riparian ecosystems,with 89 genera and 113 taxa identified,showcasing the dominance of families like Asteraceae and Lamiaceae.The study unveils the structural importance of key species such as Berberis asiatica and Artemisia nilagirica.The density,diversity,and richness of shrub and herb species vary significantly across flow conditions.Notably,altered flow conditions demonstrate resilience in vegetation structure,while diverted conditions exhibit decreased species richness and density.The study emphasizes the importance of nuanced environmental flow management for mitigating adverse effects on riparian biodiversity in the fragile Himalayan region.These findings contribute to the global discourse on dam impacts and riparian ecology,shedding light on the complexities of this dynamic relationship in a vulnerable ecosystem.
基金RAS and TEVS were supported by NERC/NSFC BETR Project NE/P013805/1.
文摘The Eastern Himalayas are renowned for their high plant diversity.To understand how this modern botanical richness formed,it is critical to investigate past plant biodiversity preserved as fossils throughout the eastern Himalayan Siwalik succession(middle Miocene-early Pleistocene).Here,we present a summary of plant diversity records that document Neogene floristic and climate changes.We do this by compiling published records of megafossil plant remains,because these offer better spatial and temporal resolution than do palynological records.Analyses of the Siwalik floral assemblages based on the distribution of the nearest living relative taxa suggest that a tropical wet evergreen forest was growing in a warm humid monsoonal climate at the deposition time.This qualitative interpretation is also corroborated by published CLAMP(Climate Leaf Analysis Multivariate Program) analyses.Here,we also reconstruct the climate by applying a new common proxy WorldClim2 calibration.This allows the detection of subtle climate differences between floral assemblages free of artefacts introduced by using different methodologies and climate calibrations.An analysis of the Siwalik floras indicates that there was a gradual change in floral composition.The lower Siwalik assemblages provide evidence of a predominance of evergreen elements.An increase in deciduous elements in the floral composition is noticed towards the close of the middle Siwalik and the beginning of the upper Siwalik formation.This change reflects a climatic difference between Miocene and Plio-Pleistocene times.This review helps us to understand under what paleoenvironmental conditions plant diversity occurred and evolved in the eastern Himalayas throughout the Cenozoic.
基金Department of Botany,Dolphin(PG)Institute of Bio-medical and Natural SciencesDepartment of Botany,DSB Campus,Kumaun University for liberal supportDepartment of Forestry and Environmental Science,DSB Campus,Kumaun University for the liberal support。
文摘While the need for understanding the effects of topographical factors on forest structure and function is well recognized,comprehensive studies are scarce.This study evaluates the effect of slope aspect and slope position on water relations and forest attributes across six forest types occurring between 400 m and 2600 m altitude in the Central Himalaya(27°-38°N).We found that predawn tree water potential and soil water potential were generally higher on moist north slope aspect(-0.78±0.05 MPa and-3.34±0.18 MPa,respectively)than dry south slope aspect(-0.82±0.18 MPa and-3.77±0.18 MPa,respectively).Across six different forests,these values were higher at hill base(-0.71±0.06 MPa and-2.77±0.19 MPa,tree predawn water potential and soil water potential,respectively)than other topographical positions.The favorable effect of north aspect and hill base was also observed in maintaining soil water and tree water potential during the dry season.Vegetation attributes,such as species richness,unique species and plant density were also generally higher on north slope and hill base than southern aspect and lowest at hill top.Across forest types,the hill base provided shelter to 46 unique species,compared to 16-18 at the other positions,thus emphasizing its importance as refugia for species to survive climate change induced perturbations.The favorable conditions of hill base position not only contribute to increase in alpha diversity,but also to extended species distributional range.
基金supported by the Geological Survey Project of China Geological Survey(Grant No.DD20211547)the Basic Survey Project of Command Center of Natural Resources Comprehensive Survey(Grant No.ZD20220508)。
文摘The widely distributed Early Cretaceous magmatism in the Tethys Himalaya(TH)of southern Tibet is related to the Kerguelen mantle plume.Associated magmatic activity products are distributed in the eastern TH,where the active age is earlier than the peak ages of the Kerguelen mantle plume.This study investigated magmatic activity of the Dingri area in the central TH which was coeval with the Kerguelen mantle plume.The intrusion in the Dingri area contains diabases and monzonites.The zircon age of diabase is 123±1 Ma,and that of monzonite is 117±1 Ma.Geochemistry and Sr-Nd isotopic analyses show that the mafic-intermediate dikes were formed in an intraplate extensional environment.The diabase is derived from the enriched lithospheric mantle and monzonite is derived from partial melting of the lower crust,with both magmatic evolutions being contaminated by crustal materials.These characteristics are similar to those of the Rajmahal-Sylhet basalt,a typical Kerguelen mantle plume product.The discovery of the Dingri mafic-intermediate dikes of the central TH suggests that the TH and Rajmahal-Sylhet Traps formed a continuous mantle plume overflow magmatic belt which was a product of the continuous eruption of the Kerguelen mantle plume.
文摘The Garhwal Himalaya is among the major repositories of immensely valuable wild edible plants and provides food security to the local population.Among the valuable plant species that grow in this region,Paeonia emodi(family Paeoniaceae)is an important wild edible species that found in temperate regions with an altitude range between 1800 and 2800 m.The species is facing a severe threat to its sustainability due to overharvesting,habitat disturbances,and a lack of effort regarding conservation.For the first time,this study investigated anthropogenic pressure,population decline perceptions in the natural habitat,and vulnerability assessment of P.emodi under selected study sites(n=23 villages).A semi structured questionnaire was used to interview approximately 45%of the local inhabitants,including herbal practitioners(Vaidhyas or Dais)of each village.On the basis of demographic characteristics,the perceptions and responses of 464 local people were documented regarding potential causes of deterioration and feasible options for sustainable utilization.Using the weight survey method,we estimated the actual amount of collection based on personal interaction and direct observation.In order to determine the threats status,a rapid vulnerability assessment(RVA)was performed and were used based on the current exploitation and usage.The present study revealed that leaf(100%)was the most frequently harvested part,followed by stem(95.65%),seed(26.09%),root(21.74%)and flower(13.04%).The village Triyuginarayan and Pothivasa recorded the highest collection scores while the purpose of the collection was mostly edible(100%),medicinal(100%),and least commercial(8.70%).According to the literature review and the present survey,the RVA(total=21)is categorized as category II(intermediate side of the RVA index),indicating a degree of vulnerability.The study revealed that P.emodi faces extinction in the Garhwal Himalayas.Growing this species through agro-production techniques may alleviate the pressure on the existing population as a result of the availability of raw materials for commercial and household uses.These findings will provide an effective framework for conservation and management decisions and plans.
基金the University Grant Commission, New Delhi (3090/ (NET–DEC.2014) for financial support during field visitsthe Department of Science and Technology, Govt of India, for sponsoring the project “Himalayan Cryosphere: Science and Society”
文摘Glacier shrinkage is a globally occurring phenomena.High-resolution change detection based on frequent mapping and monitoring of high-altitude glaciers is necessary to precisely evaluate future water availability and to understand glacier evolution under different climatic scenarios in the Hindukush-Karakoram-Himalayan(HKH)region.This also holds true for the Bhaga basin of the western Himalaya.This study investigates glacier and glacier lake changes in the Bhaga basin,over the last five decades based on satellite imagery including Corona KH4(1971),Landsat 7 Enhanced Thematic Mapper Plus(ETM+;2000),Linear Imaging Self-Scanning Sensor(LISS Ⅳ;2013),and Sentinel 2(2020).Regional temperature and precipitation trends were evaluated from gridded climatic datasets(1900–2020).In the Bhaga basin 306 glaciers(>0.2 km^(2))were mapped with a total area of 360.3±4.0 km^(2),of which 55.7±0.6 km^(2)was covered with debris in 2013.The total glacier covered area decreased by∼8.2±1.5%(0.16±0.03%yr-1)during the entire observation period 1971–2020,with noticeable heterogeneity between tributary watersheds.In the past two decades(2000–2020),the deglaciation rate has increased significantly(0.25%yr-1)compared to the previous decades(1971–2000;0.12%yr-1).Glacier lake area increased by 0.6±0.1 km^(2)(0.012 km^(2)yr-1)between 1971 and 2020.The NCEP/NCAR climatic data reveals an increase of 0.63℃in temperature and a decrease of 6.39 mm in precipitation for the period 1948–2018.In comparison,APHRODITE data shows an increasing trend in temperature of 1.14℃between 1961 and 2015 and decreasing trend in precipitation of 31 mm between 1951 and 2007.Both NCEP/NCAR and APHRODITE data reveal significant temperature increase and precipitation decrease since the 1990s,which have probably augmented ice loss in the Bhaga basin during the early 21st century.
文摘Glacier response patterns at the catchment scale are highly heterogeneous and defined by a complex interplay of various dynamics and surface factors.Previous studies have explained heterogeneous responses in qualitative ways but quantitative assessment is lacking yet where an intrazone homogeneous climate assumption can be valid.Hence,in the current study,the reason for heterogeneous mass balance has been explained in quantitative methods using a multiple linear regression model in the Sikkim Himalayan region.At first,the topographical parameters are selected from previously published studies,then the most significant topographical and geomorphological parameters are selected with backward stepwise subset selection methods.Finally,the contributions of selected parameters are calculated by least square methods.The results show that,the magnitude of mass balance lies between-0.003±0.24 to-1.029±0.24 m.w.e.a^(-1) between 2000 and 2020 in the Sikkim Himalaya region.Also,the study shows that,out of the terminus type of the glacier,glacier area,debris cover,ice-mixed debris,slope,aspect,mean elevation,and snout elevation of the glaciers,only the terminus type and mean elevation of the glacier are significantly altering the glacier mass balance in the Sikkim Himalayan region.Mathematically,the mass loss is approximately 0.40 m.w.e.a^(-1) higher in the lake-terminating glaciers compared to the land-terminating glaciers in the same elevation zone.On the other hand,a thousand meters mean elevation drop is associated with 0.179 m.w.e.a-1of mass loss despite the terminus type of the glaciers.In the current study,the model using the terminus type of the glaciers and the mean elevation of the glaciers explains 76% of fluctuation of mass balance in the Sikkim Himalayan region.
文摘Leishmaniasis is a vector-borne parasitic disease affecting millions of people worldwide.However,in the last decade,the number of cases has been reduced from well-documented endemic parts,but sporadic cases have been reported widely from various non-endemic areas,especially from the southern Himalayan zone.This raises concerns about the emergence of new ecological niches.This warrants a critical evaluation of key factors causing this rapid spread and possibly indigenous transmission.This mini-review article is aimed to briefly address the parasite,the vector,and the environmental aspects in the transmission of leishmaniasis in these new foci against a background of worldwide endemic leishmaniasis with a special focus on the southern Himalayan zone.As the lack of knowledge about the causative parasites,vectors,reservoir hosts,atypical presentations,and their management make the problem serious and may lead to the emergence of public health issues.The present works also reviewed the existing information regarding clinical variations,diagnostic methods,treatment,its outcome,and ignite for further research in these aspects of the disease.
基金The authors are thankful to the Director,Birbal Sahni Institute of Palaeosciences,Lucknow for constant support and providing infrastructural facilities.
文摘The fragmented pattern and the rapidly declining preservation of older glacial features/evidences limits the precision,with which glacial chronologies can be established.The challenge is exacerbated by the scarcity of datable material and limitations of dating methods.Nevertheless,the preserved glacial landforms have been fairly utilized to establish glacial chronologies from different sectors of the Indian Himalayas.The existing Himalayan glacial chrono-stratigraphies have revealed that in a single valley,past glacial advances rarely surpass four stages.Thus,local and regional glacial chronologies must be synthesized to understand glacial dynamics and potential forcing factors.This research presents an overview of glacier responses to climate variations revealed by glacial chrono-stratigraphies in the western Indian Himalayan region over the Quaternary(late).The synthesis demonstrated that,although the glacial advances were sporadic,glaciers in western Himalayas generally advanced during the Marine isotope stage(MIS)-3/4,MIS-2,late glacial,Younger Dryas(YD)and Holocene periods.The Holocene has witnessed multiple glacial advances and the scatter is significant.While previous glacial research revealed that Himalayan glaciers were out of phase with the global last glacial maximum(gLGM),weak Indian Summer Monsoon(ISM)has been implicated(ISM was reduced by roughly 20%).Recent research,however,has shown that gLGM glaciation responded to the global cooling associated with the enhanced mid-latitude westerlies(MLW).Further,the magnitude of gLGM glacier advance varied along and across the Himalayas particularly the transitional valleys located between the ISM and MLW influence.It is also evident that both the ISM and MLW have governed the late Quaternary glacial advances in the western Himalayan region.However,the responses of glaciers to ISM changes are more prominent.The insights gained from this synthesis will help us understand the dynamics of glacier response to climate change,which will be valuable for future climate modelling.
文摘Sikkim Himalaya hosts critical water resources such as glacial,rain,and snow-fed springs and lakes.Climate change is adversely affecting these resources in various ways,and elevation-dependent warming is prominent among them.This study is a discussion of the elevation-dependent warming(EDW),snowfall shift,and precipitation variability over Sikkim Himalaya using a high-resolution ERA5-land dataset.Furthermore,the findings show that the Sikkim Himalaya region is experiencing a warming trend from south to north.The majority of the Sikkim Himalayan region shows a declining trend in snowfall.A positive advancement in snowfall trend(at a rate of 1 mm per decade)has been noticed above 4500 meters.The S/P ratio indicates a shift in snowfall patterns,moving from lower elevations to much higher regions.This suggests that snowfall has also transitioned from Lachung and Lachen(3600 m)to higher elevated areas.Moreover,the seasonal shifting of snowfall in the recent decade is seen from January-March(JFM)to February-April(FMA).Subsequently,the preceding 21 years are being marked by a significant spatiotemporal change in temperature,precipitation,and snowfall.The potent negative correlation coefficient between temperature and snowfall(–0.9),temperature and S/P ratio(–0.5)suggested the changing nature of snowfall from solid to liquid,which further resulted in increased lower elevation precipitation.The entire Sikkim region is transitioning from a cold-dry to a warm-wet weather pattern.In the climate change scenario,a drop in the S/P ratio with altitude will continue to explain the rise in temperature over mountainous regions.
文摘The current article is an opinion on the sensitivity of high mountain regions which are the most fragile,sensitive and vulnerable to ongoing climate change.Its impacts are especially severe on the high mountain communities owing to their weak socio-economic profile,limited livelihood resources and agricultural land.The melting of glaciers and changes in the snow cover under the climate change scenario is leading to the scarcity of freshwater supplies,affecting both local and downstream communities.Changes in the precipitation patterns have been suggested to cause droughts,impact restricted agriculture,and limit the availability of water for domestic use.Additionally,the high mountain areas contain distinct flora and fauna,and climate change is not just altering them,but also has resulted in biodiversity loss as species are unable to adapt to the changing climate.Because of its higher altitudes and semi-arid to arid climate,the consequences of climate change are more evident in the higher Himalayas.Climate change is affecting the availability of key resources,such as freshwater and agriculture and pasture lands,resulting in food and water insecurity and their reliance on imports from other regions.As a result,high mountain communities in the Himalayas are progressively shifting to higher glacier valleys in search of suitable cultivable land with adequate irrigation.People are engaging in agro-pastoral activities around thermokarst lakes(Oasis)atop rock glaciers as part of this endeavour.Such actions underscore the crucial role of rock glaciers in dealing with and adjusting to the consequences of climate change.Despite its relevance,rock glacier research in the Himalayan region is still in its infancy.The purpose of this work is to emphasise the significance of these major climate-resilient water resources,as well as the methodology that must be adopted for their systematic and compressive investigations.
文摘The Eastern Sikkim area forming a part of the Lesser Himalaya is located between 27°10′～27°30′N latitudes and 88°25′～88°40′E longitudes (750km 2). The previous workers agreed that a domal structure is present in Sikkim which is constituted by low to high grade metamorphic rocks characterised by inverted metamorphism. The rocks were repeatedly deformed and were metamorphosed at about 550 to 770℃ (550 to 750MPa). Geologically, the oldest rocks of Eastern Sikkim are represented by Darjeeling Formation showing medium to high grade metamorphism. It is followed by low grade Daling Formation which is characterised by tectonic wedges of Lingtse gneiss. The potassic syenite intrusive i.e. the Sikkim igneous formation is youngest rock type of the area. The Darjeeling Formation associated with amphibolite bands consists of kyanite\|sillimanite, staurolite and garnet zones, while the Daling Formation is characterised by low grade chloritoid and chlorite zones. Lingtse Formation is gneissic in which patches of retrograded and sheared garnet schists are present. Intrusions of potassic syenites (Sikkim Formation) occur in the form of oval and concordant bodies. The F 1, F 2 and F 3 folds are well developed in rocks of Eastern Sikkim area.. The F 1 folds are rootless, tightly isoclinal or reclined and highly obliterated in their attitude. The F 2 folds belong to class IC of Ramsay (1967). Their interlimb angles vary from 20～50 degrees. Intersection lineation due to S 0/S 1 and S 2 surfaces is parallel to the F 2 folds axis. Third generation structures are represented by open to moderately tight and kinked folds. Superimposition of F 3 folds on F 2 folds resulted into type II interference pattern of Ramsay (1967). Structural analysis of these folds have revealed that F 2 folds are non\|cylindrical. The kink or F 3 folds were possibly responsible for the formation of a megakink resembling with the domal structure. The repeatedly deformed rocks of Eastern Sikkim area were folded, faulted, sheared/thrusted during the Himalayan orogeny. The Main Central Thrust (M C T) is actually a ductile shear zone and was subjected to imbrication during later phases of F 2 folding.
文摘The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.
文摘New monazite U\|Pb geochronological data from the Everest region suggest that 20～25Ma elapsed between the initial India—Asia collision and kyanite\|sillimanite grade metamorphism. Our results indicate a two\|phase metamorphic history, with peak Barrovian metamorphism at (32 2±0 4)Ma and a later high\|temperature, low\|pressure event (620℃, 400MPa) at (22 7±0 2)Ma.. Emplacement and crystallization of the Everest granite subsequently occurred at 20 5～21 3Ma. The monazite crystallization ages that differ by 10Ma are recorded in two structurally adjacent rocks of different lithology, which have the same post collisional p—T history.. Scanning electron microscopy reveals that the younger monazite is elaborately shaped and grew in close association with apatite at grain boundaries and triple junctions, suggesting that growth was stimulated by a change in the fluid regime. The older monazite is euhedral, is not associated with apatite, and is commonly armoured within silicate minerals. During the low\|pressure metamorphic event, the armouring protected the older monazites, and a lack of excess apatite in this sample prevented new growth. Textural relationships suggest that apatite is one of the necessary monazite\|producing reactants, and spots within monazite that are rich in Ca, Fe, Al and Si suggest that allanite acted as a preexisting rare earth element host. We propose a simplified reaction for monazite crystallization based on this evidence.
基金sponsored by National Program on Key Basic Research Project(973 Program, Grant No. 2016YFC0600308)the China Geological Survey(Grant No. DD20160015)
文摘The Upper Triassic flysch sediments(Nieru Formation and Langjiexue Group)exposed in the Eastern Tethyan Himalayan Sequence are crucial for unraveling the controversial paleogeography and paleotectonics of the Himalayan orogen.This work reports new detrital zircon U-Pb ages and whole-rock geochemical data for clastic rocks from flysch strata in the Shannan area.The mineral modal composition data suggest that these units were mainly sourced from recycled orogen provenances.The chemical compositions of the sandstones in the strata are similar to the chemical composition of upper continental crust.These rocks have relatively low Chemical Index of Alteration values(with an average of 62)and Index of Compositional Variability values(0.69),indicating that they experienced weak weathering and were mainly derived from a mature source.The geochemical compositions of the Upper Triassic strata are similar to those of graywackes from continental island arcs and are indicative of an acidicintermediate igneous source.Furthermore,hornblende and feldspar experienced decomposition in the provenance,and the sediment became enriched in zircon and monazite during sediment transport.The detrital zircons in the strata feature two main age peaks at 225-275 Ma and 500-600 Ma,nearly continuous Paleoproterozoic to Neoproterozoic ages,and a broad inconspicuous cluster in the Tonian-Stenian(800-1200 Ma).The detrital zircons from the Upper Triassic sandstones in the study area lack peaks at 300-325 Ma(characteristic of the Lhasa block)and 1150-1200 Ma(characteristic of the Lhasa and West Australia blocks).Therefore,neither the Lhasa block nor the West Australia blocks likely acted as the main provenance of the Upper Triassic strata.Newly discovered Permian-Triassic basalt and mafic dikes in the Himalayas could have provided the 225-275 Ma detrital zircons.Therefore,Indian and Himalayan units were the main provenances of the flysch strata.The Tethyan Himalaya was part of the northern passive margin and was not an exotic terrane separated from India during the Permian to Early Cretaceous.This evidence suggests that the Neo-Tethyan ocean opened prior to the Late Triassic and that the Upper Triassic deposits were derived from continental crustal fragments adjacent to the northern passive continental margin of Greater India.
文摘Prevailing dogma asserts that the uplift of Tibet, the onset of the Asian monsoon system and high biodiversity in southern Asia are linked, and that all occurred after 23 million years ago in the Neogene.Here, spanning the last 60 million years of Earth history, the geological, climatological and palaeontological evidence for this linkage is reviewed. The principal conclusions are that: 1) A proto-Tibetan highland existed well before the Neogene and that an Andean type topography with surface elevations of at least 4.5 km existed at the start of the Eocene, before final closure of the Tethys Ocean that separated India from Eurasia. 2) The Himalaya were formed not at the start of the India-Eurasia collision, but after much of Tibet had achieved its present elevation. The Himalaya built against a pre-existing proto-Tibetan highland and only projected above the average height of the plateau after approximately 15 Ma. 3)Monsoon climates have existed across southern Asia for the whole of the Cenozoic, and probably for a lot longer, but that they were of the kind generated by seasonal migrations of the Inter-tropical Convergence Zone. 4) The projection of the High Himalaya above the Tibetan Plateau at about 15 Ma coincides with the development of the modern South Asia Monsoon. 5) The East Asia monsoon became established in its present form about the same time as a consequence of topographic changes in northern Tibet and elsewhere in Asia, the loss of moisture sources in the Asian interior and the development of a strong winter Siberian high as global temperatures declined. 6) New radiometric dates of palaeontological finds point to southern Asia's high biodiversity originating in the Paleogene, not the Neogene.
文摘Geological evidences have indicated large\|scale crustal shortening by thrust faultings in Himalaya , such as MCT and MBT. The thrust faulting near Yarlungzampbo suture was also observed. However, it is still unknown to what depth those thrust faultings have been going down into the crust or upper mantle . Seismological evidences indicate that the thrust faultings in Himalaya and southern Tibet have extended to a depth of 80 to 100km , and stopped there. The thrust faultings underneath MCT MBT and Yarlungzampbo suture are closely related to the multiple crustal subductions in Himalaya and southern Tibet. It provides important constraints for the collision process between India and Eurasia. The incomplete crustal subductions in this region suggest that the impinging Indian crust is too light to prevent it going further down, and retreat of crustal subduction is required for the continuing northward movement of the Indian plate. The multiple crustal subductions are compatible to the multiple episodes of the geological activities in Himalaya and southern Tibet. At first, the crustal subduction was produced at Yarlungzampbo suture , and stopped at a depth of 80～100km. Then, it migrated to the south, other new crustal subductions would start successively at MCT and MBT respectively. They stopped at a depth of 80 to 100km also. Beside the north\|dipping seismic zones in Himalaya and Yarlungzamp bo suture, another gentle south\|dipping seismic zone,extending from Tangula Shan at the surface to the Moho at Yarlungzampbo suture was also observed. It can be interpreted to be an obduction at Tangula Shan. The multiple incomplete crustal subductions in Himalaya and Yarlungzampbo suture highly imply that the impinging Indian crust has been splitted apart from its upper\|most mantle, which may b e subducted deeper into the Eurasian mantle.
文摘Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between Indian and Asian continents during Cenozoic.Based on geometric and kinematic mapping of the major boundary or regional faults (Dongjug—Mainling(1), Anigiao(2) and Jali(3), Guyu(4) faults in EHS, Ailaoshan—Red River(5), Lancangjiang(6), Gaoligong(7), Binlangjiang(8) and Magok(9) faults in WSY) (see Fig.1), especially on abundant geochronological dating of the mylonitic rocks along these faults, and coupled with magmato\|metamorphic sequences of this region, we try to deal with the temporal and spatial relationships of collisional process to answer questions such as: (1) when did collision start ? (2) is thrusting as a initial and dominant deformation mode to absorb the crustal shortening after suturing, or earlier thrusting usually followed by large\|scale strike\|slip faults? (3) are the two structural patterns coeval at times, or do they occur alternatively during deformation history? (4) are the collisional and associate uplift processes a continuous one or periodic? Insight into such questions is crucial for better understanding of the continental deformation and testing the models available or constraining a new one.
