A series of collisions among most of the continental fragments between 2.1 Ga and 1.8 Ga culminated in the assembly of the Columbia supercontinent. Vestiges of reworked Northern Indian Continental Margin, involved in the Columbia supercontinent assembly, are preserved and known as the 'Paleoproterozoic high-grade metapelitic gneisses in the Askot Klippe' of NW Lesser Himalaya. We report new whole-rock geochemistry, inverse and forward geothermobarometric modeling, isochemical phase diagram modeling, and U-Pb zircon dating of metapelitic schists and gneisses to decode the multiple metamorphic histories in Lesser Himalayan fold-thrust. We identify two metamorphic events that mark the Columbia Supercontinent assembly's accretion phases: an earlier ca. 1.85 Ga age related to the first metamorphic episode and a second age of ca. 1.62 Ga associated with the youngest reported collisional event related to subduction followed by accretion of crust and attendant crustal anatexis. The earlier event reached upper green-schist facies metamorphism during which garnet cores crystallized, whereas the second event indicates amphibolite-granulite peak metamorphic conditions. Our results show that the amalgamation of Columbia persisted until at least ca. 1.62 Ga in the northwestern Lesser Himalaya, indicating tectonic continuity between the northern Indian continental margin, the Aravalli-Delhi Mobile Belt, and the Eastern Cathaysia Block-key elements in the final Paleoproterozoic assembly of the Columbia supercontinent.

Paleoproterozoic granitoids are important rock types all along the Lesser Himalayan belt and provide key constraints for understanding the evolution of the northern Indian continental margin and its position within the Columbia supercontinent assembly. The Paleoproterozoic Ramgarh mylonitic granitoids of the Baijnath klippe in the Inner Kumaun Lesser Himalayan Sequence show pervasive mylonitization, with augen-shaped porphyroclasts of feldspar and quartz, which characterize the Ramgarh mylonitic granitoids throughout the Lesser Himalaya. We present petrological and whole-rock geochemical data from the Ramgarh mylonitic granitoids of the Baijnath klippe to evaluate their petrogenesis and geodynamic implications. These monzonitic granitoids are geochemically peraluminous with high K2O and MgO along with enrichment in LILE (Rb, K, Pb, and Th) and depletion in Ba, P, Nb, and Ti, along with moderately negative Eu anomalies. Geochemically, the Ramgarh granitoids are classified as I-type (Igneous arc-type) granite. Zircon U-Pb geochronology from the Kausani body yields a crystallization age of similar to 1866 Ma. The granitoids are interpreted to have formed by a high degree of partial melting of underplated lower-crustal material during the early phase of slab rollback or break-off of a subducting slab. This magmatic event likely preceded the emplacement of the post-collisional extensional magmatism, suggesting an evolving subduction-accretion system. The geochemical and geochronological data support an active continental margin setting along the northern Indian plate margin at similar to 1.8 Ga. This suggests that these oldest granitoids represent a magmatic arc developed in a subduction zone setting during the assembly of the Columbia supercontinent. Later, during the Cenozoic Himalayan orogeny, the granitoids were thrust over the Lesser Himalayan Sequence as nappes and klippen.

In Kumaun Lesser Himalaya, North Ramgarh Thrust and South Ramgarh Thrust define the northern and southern boundaries of the Almora Nappe. The Almora Nappe consists of two tectono-stratigraphic units, viz. the Ramgarh Group and the Almora Group. The Ramgarh Group consists of mylonitised granite gneisses capped by low-grade metamorphic rocks and the Almora Group consists of an interbanded sequence of metapelites and metapsammites progressively metamorphosed from the greenschist to upper amphibolite facies conditions. The Almora Group rocks comprise quartzites, garnet-mica schists, and K-feldspar–sillimanite gneisses. The garnet-mica schists are coarse to medium-grained, with well-developed foliation defined by chlorite-biotite-muscovite-garnet-plagioclase-quartz mineral assemblage, and the accessory minerals are apatite and zircon. The pelitic gneisses consist of garnet, kyanite, cordierite, sillimanite, and K-feldspar. Garnet is a common and important mineral in these metamorphic rocks to constrain P-T conditions. In this study, we specifically focus on the textural details of garnets from the schists and gneisses of the Almora Group. The most common garnet is type II garnet which is synkinematic with S-shaped inclusions of quartz and biotite, while the older type-I garnets occur as stretched out grains in the matrix with the stretch direction generally parallel to the foliation. The garnet porphyroblasts are euhedral to subhedral and consist of quartz, plagioclase, muscovite, and apatite inclusions, which are wrapped around by muscovite and biotite lepidoblasts. The hematite leachings are observed around the periphery of the garnet porphyroblasts that suggest high fO2 in the last stages of garnet growth. The micas microfolded in a few samples, with the presence of quartz in the folded hinge region. The garnets can be classified into at least two generations based on textural and petrographic attributes. Moreover, the presence of an idioblastic rim in the garnets suggests that the later phase of metamorphism outlasted the deformation. The occurrence of two generations of garnet i.e. garnet within garnet documented by (Joshi & Tiwari, 2004; Joshi & Tiwari, 2009) suggests a hiatus in crystallization and the associated metamorphic processes are likely attributed to two generations of pre-Himalayan metamorphisms.

ABSTRACT The Cenozoic Himalayan orogeny resulted from the continental collision between the Tibetan block and the northern Indian Precambrian shield. The latter, replete with evidence of Columbian supercontinent assembly, likely comprised the north Indian continental margin that was reworked mechanically and thermally during the Himalayan orogeny, and still survives as Precambrian vestiges in the Himalaya. Parts of this Paleoproterozoic crust, which now occur as nappes and klippen, were tectonically transported by the Main Central Thrust southwards over the Lesser Himalayan sedimentaries during the orogeny. The Absence of Columbian metamorphic signatures in these thrust sheets has intrigued geologists for long. We present evidence for a Middle Orosirian metamorphic event from the pelitic gneisses of the Almora Group in the Baijnath Klippe from NW Himalaya. The physical conditions of metamorphism have been inferred using mineral chemistry, bulk‐rock chemistry, and phase section modeling using Perple_X software in the MnNKCFMASHT model system. Zircon U–Pb geochronology for the Dangoli pelitic gneisses yielded a robust upper intercept at 1891 ± 12.82 Ma. The P–T phase diagram indicates that the peak mineral assemblage stabilized in the P–T range of 0.41–0.46 GPa and 675°C–700°C suggesting upper amphibolite facies metamorphism. Integrated metamorphic and geochronological results indicate that the Dangoli pelitic gneisses were derived by muscovite dehydration melting of metasediments during the peak metamorphism related to syn‐collisional setting broadly coeval with the Paleoproterozoic magmatism during the Columbia supercontinent assembly. The evidence for definite involvement of Paleoproterozoic high‐grade metamorphic rocks of the northern Indian shield in the Himalayan orogeny is being documented.

Paleoproterozoic granitoids of the lesser Himalayan belt are keys to understanding the evolution of the northern Indian continental margin and its position in the Columbia supercontinent assembly. We present whole-rock chemistry and zircon U-Pb geochronological data for Gwaldam Biotite Granite (GBGr) from the Baijnath Klippe (BK) in Kumaun Himalaya to elucidate their petrogenesis and geodynamic implications. Granites are characterized by ferroan, weakly peraluminous nature with high SiO(2 )and K2O contents, enrichment in LILE (Rb, Th, K and Pb), and depletion in Ba, Nb, P, Hf and Ti. Granites show enrichment in light rare earth element relative to heavy rare earth elements and pronounced negative Eu anomalies. Such chemistry suggests typical A-type granite with high Y/Nb >2 values that characterize it as A(2)-type granite. Zircon U-Pb ages for the granite yield upper intercept at 1900 +/- 3 Ma (core) and 1854 +/- 2 Ma (rim). Integrating the chemical and geochronological data, we propose a two-stage evolution model for the area. In the GBGr, the similar to 1900 Ma date of zircon core is likely the date of crystallization of the melts presumably formed during the first extensional stage at uppermost mantle - lower crust levels caused by slab break-off/rollback, which followed a post-collisional setting. The second incipient rifting stage produced melt that entrained the zircon cores (similar to 1900 Ma) during its ascendance and crystallized as the GBGr at similar to 1854 Ma when the zircon rims crystallized. It is further proposed that the Paleoproterozoic Northern Indian continental margin later underwent at least two crustal extensions during the Columbia supercontinent agglomeration.

Plagioclase ultraphyric basalts (PUBs) are an important unit of the Abor magmatic complex (AMC) of the eastern Himalaya, containing ≥35 vol% plagioclase phenocrysts. Apart from the eastern region, PUBs have not been reported in any other part of the Himalayas. However, very little information is available about their origin and significance in the evolution of the eastern margin of the Indian plate and the Himalayan orogeny. In this contribution, we present the first zircon UPb age data of the PUBs along with whole-rock geochemistry, SrNd isotopic ratios, mineral chemistry, and quantitative textural analysis, to understand the evolutionary history of the AMC and subsurface magma chamber activities. The PUBs formed from highly evolved magma (<6 MgO wt%), having high Fe2O3 (9.06–12.29 wt%) and Ti/Y ratios (>500). Their εNd (t) values (−0.02 to +2.66) suggest plume magma source. A small difference in anorthite contents (<5 mol%) is observed from the thick core (An47–58) with lower anorthite contents towards the rim (An34–47) of the plagioclase phenocrysts, which is an indication of weakly zoned characteristics. Crystal size distribution shows a non-linear and concave upward trend with a relatively gentler slope towards the coarser plagioclase populations, which can be attributed to the hybrid crystallization of plagioclase-bearing magma and its subsequent differentiation with cumulates of plagioclase inside the magma chamber. The zircon UPb age of these PUBs records two magmatic events - Early Paleozoic (505–473 Ma) at the core and Early Cretaceous (134–126 Ma) at the rim that are consistent with the previously proposed magmatic events of AMC with Gondwana assembly and break-up. Encounter of such dual ages in zircons does not support the usual condition of PUBs formation through crystal floatation in a slow cooling process of a single magma chamber. Therefore, considering the evidences observed in crystal size distribution, core-rim anorthite variation, geochemistry, and age data, we propose that the PUBs of AMC, eastern Himalaya were formed due to injection of a hot and young magma during the Early Cretaceous into an old and cold mush zone containing pre-existing plagioclase phenocrysts formed during the Early Paleozoic. The results further support that the newly injected magma formed the rim of the plagioclase phenocrysts and the groundmass of the PUBs.

The semi-arid Ladakh region in the Trans Himalaya forms an environmental boundary between North Atlantic and monsoon forcings. Its location in the transient setting of these two climate systems enables to attest slight changes in the dynamics of these components of atmospheric circulation. Variation in climatic conditions from 19.6 to 6.1 ka using multi-proxy investigation (mineral magnetism, stable carbon isotope, palaeoprecipitation, sediment grainsize end member analysis, clay mineralogy and TOC) is studied from Khalsi palaeolake deposit in Ladakh. Considering the inherent uncertainty of radiocarbon chronology, the present study provides millennial to multi-centennial scale resolution of climate variation from the sediment sequence. The results indicate cold arid climate influenced by Westerly circulation for the last 19.6 to 11.1 ka, thereafter from 11.1 to 7.5 ka, monsoon forcings dominated the climate of the region, following the orbitally controlled solar insolation that influenced the position of ITCZ and formed the key driver of the variability of these atmospheric circulations. A short wet phase from-17.4 to 16.5 ka within the dominant Westerly period is attributed to the early wet phase of two-fold H1 event. Westerly regained strength from 7.5 to 6.1 ka during the mid-Holocene coinciding with decreasing insolation, weakening monsoon and enhanced El Nin & SIM;o activities.

Landform geomorphology and glacial lake deposits in the largest drainage basin of the Ladakh Range i.e. Chang La-Tangtse basin were studied to infer their palaeoclimatic significance. The grain size, mineral magnetism, percentage loss on ignition (%LOI) and organic carbon stable isotope (delta C-13) data in combination with total organic carbon (TOC) supported by AMS C-14 (calibrated) dates of a 190 cm long section from the Chang La-Tsoltak palaeolake provides a climatic record since the last similar to 7075 cal yr BP. The chi lf, chi ARM, and SIRM values suggest that the catchment-derived palaeolake sediments predominantly contain magnetically "soft" minerals like magnetite and maghemite. The delta C-13 values range between -21 and -24 parts per thousand with an average of -22 parts per thousand which suggests a mixed C3-C4 plant signature and water stressed ecosystem. The relatively small variations in the delta C-13 values of organic matter in the entire lake profile suggest a stable climatic condition. The prominent effect of westerlies is seen between 7075 and 6040 cal yr BP with huge detrital influx at the lake bottom indi-cating a glacial advancement in the region. The affect of Mid-Holocene warm period is evident at 6040 cal yr BP with the advent of ISM. Paradigm shifts in the proxy values are observed at 5710, 4890, 3435, and 2800 cal yr BP. The influence of westerlies gradually reduces at 2800 cal yr BP. The landscape evolution and the climatic variations in the Trans-Himalaya are primarily governed by westerlies and do not correspond to the Indian monsoon variability records, particularly during the Mid-Holocene Thermal Maxima. Several other regions of the Ladakh Range also record similar climatic variations, indicating that the palaeolake sediments also reflect regional climate variations.

Abstract We report new U–Pb zircon ages for mafic plutonic (gabbro) and volcanic (andesite) rocks, along with the whole-rock chemistry of a mafic–felsic suite of volcanic rocks from the Siang window of the Eastern Himalayan Syntaxis, NE India. Field relationships, and mineralogical and geochemical characteristics, of the studied mafic–intermediate–felsic rocks suggest their co-magmatic linkage that was generated in an extensional tectonic environment. Incompatible trace elements and low concentrations of large ion lithophile elements (LILEs) and REE behaviour reflect both the enriched nature of the mafic rocks and the limited influence of crustal contamination in their genesis. Partial melting and fractional crystallization processes have played a major role during the genesis of these felsic volcanics from the parental mafic magma. The laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb ages suggest that the mafic plutonic rock was emplaced at c. 121.18 ± 1 Ma and intermediate volcanic rock was emplaced at c. 135.48 ± 0.50 Ma during the Early Cretaceous period. The new ages are consistent with earlier reported zircon U–Pb ages (133.0 ± 1.9–130.7 ± 1.8 Ma) of felsic volcanic rocks from the present study area. Our new field observations, and mineralogical and geochemical characteristics, in conjunction with the U–Pb isotopic database suggest that the major magmatic event in the core of the Siang window of the Eastern Himalaya is coeval with the Rajmahal–Sylhet–Mikir–Shillong flood basalts of eastern and northeastern India, and the Comei–Bunbury Large Igneous Province of southeastern Tibet and SW Australia. These events are related to the break-up of eastern Gondwana and outbreak of the Kerguelen plume.

In the present study, inner Kumaun Himalayan region between village Jauljibi and Dobaat along the Kali river has been studied to understand the causes and the distribution of landslides in the area. Various geomorphic indices such as longitudinal and topographic swath profile, stream length gradient index, steepness index, and valley floor width to valley height ratio have been extracted for interpreting the active tectonics of the region, and the topographic bedding plane intersection angle (TOBIA) index for the disposition of the bedding or foliation planes of the rocks with respect to the terrain. In addition, the active nature of the thrusts and faults in the region has been interpreted with the offsets or deflection of the river terraces along these thrusts and faults. Interrelationships among these indices and the spatial distribution of landslide indicate that the region between Dharchula and Dobaat is the most tectonically active region as indicated by the presence of Dharchula Fault, Lasku Fault and South Chhiplakot Thrust along with the abnormally high steepness index and knickpoints in the region. Other regions of active tectonics are Dhap—Kalika and Jauljibi—Baniyagaon regions due to Ghatibagarh Kalika Fault, and Berinag Thrust and Rauntis Fault, respectively. In addition it has been reported that the density of landslides in the cataclinal slopes is higher as compared to landslides in the orthoclinal and anaclinal slopes, indicating the role of the disposition of the rocks with respect to the terrain in the spatial distribution of landslides in the study area.

The Indian sub-continent was an integral part of the Gondwana supercontinent with multiple magmatic episodes during the Gondwana assembly and break-up events. However, most of these vital records to understand the past magmatism were obliterated during the Himalayan orogeny due to the subduction of the Indian plate. In this contribution, we attempt to tackle this issue by investigating the Abor magmatic rocks from the eastern Himalayan syntaxis, which are likely to represent the leftover fragments of the eastern Gondwana continental margin. This study uses zircon U-Pb dating, whole-rock geochemistry, and Sr-Nd isotopic ratios data of the mafic intrusive and felsic volcanic rocks of the Abor magmatism. The mafic intrusive rocks have zircon ages of 500-473 Ma, while the felsic rocks yield ages of 145- 132 Ma, indicating two temporally separated episodes of magmatism. The mafic intrusives are subalkaline/tholeiitic (Nb/Y < 0.65), with high TiO2 (1.63-3.42 wt%) and ocean island basalt to enrichedmid oceanic ridge basalt affinities. A relatively narrow range of initial 87Sr/86Sr (0.703887-0.705513), 143Nd/144Nd (0.511978-0.512118), and eNd(t) (-0.323-+2.43) of the mafic intrusives suggest fractional crystallization with negligible crustal contamination, generated by low degree (-3-13 %) partial melting of a primitive mantle (garnet and spinel lherzolite). The felsic rocks display low MgO (0.38-1.17 wt%), CaO (1.06-5.31 wt%), LREE and LILE (Rb, K, Pb) enrichment, depletion in HREE, Sr, Nb, Ti, with strong negative Eu-anomaly (0.48-0.73), high initial 87Sr/86Sr (0.707878-0.717650), and negative eNd(t) (-14.35 to -9.21), suggesting A-type felsic magmatism. The older mafic intrusions were thus attributed to the events of the Gondwana assembly and were inferred to form in an extensional passive margin during the early Paleozoic. However, the younger felsic rocks were likely to have been generated by the interaction of the upwelling Kerguelen mantle plume and the pre-existing crust during the initiation of the eastern Gondwana break-up during the early Cretaceous. Our new findings reveal that two episodic magmatic events related to the eastern Gondwana assembly and the subsequent Gondwana break-up are responsible for the magmatism in the Siang window of eastern Himalayan syntaxis, northeast India. (c) 2022 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.

The geochemistry of dolomite in part of the Thanagazi Formation in the Mesoproterozoic Alwar Basin has been studied employing major and trace elements, including rare earth elements (REEs) to understand their provenance and paleoweathering conditions. In the current study, two distinct types of dolomites were identified viz. amorphous and crystalline. Various geochemical discriminants such as SiO2 vs Al2O3 and CaO vs MgO indicate that the dolomites were originated from sedimentary sources with substantial metasomatic and biogenic contributions. Geochemical constraints from plots of Fe2O3/Al2O3 vs. Al2O3/(Al2O3+Fe2O3) and rare earth element compositions for provenance signatures suggest likely deposition of dolomites in shallow marine sedimentary environment. Based on geothermometric estimates and base metal concentrations in dolomites, it is inferred that the mixing of sediments derived from two different sources (metasomatic and biogenic) were likely responsible for the dolomitization in the Thanagazi Formation of the Mesoproterozoic Alwar Basin.

The study focuses on the preparation of landslide susceptibility maps in the Kali River valley, Kumaun Himalaya using three machine learning algorithms, namely K-nearest neighbour (KNN), random forest (RF) and extreme gradient boosting (XGB). Fifteen landslide conditioning factors (LCFs) were selected and an inventory of 368 landslides was used for the analysis. Multicollinearity analysis using the variation inflation factor, tolerance and Pearson correlation coefficient (PCC) depicted less to no similarity between all factors. Evaluation of variable importance suggests LCFs such as slope, elevation and distance to thrust contributed significantly and consistently for all three models. Model accuracy was determined and compared using the area under the receiver operating characteristic curve and other statistical signifiers like accuracy, sensitivity, F-measure, accuracy, specificity and recall. The results show that the ensemble algorithms, XGB and RF, yield higher accuracy of approximately 85% compared to the KNN model with 81% accuracy.

The Indus River valley has frequently reorganized itself to attain geomorphic equilibrium during the Late Quaternary. In this regard, significant advances have been made towards the understanding of the response of landform/ landscape to climate (exogenic) forcings. However, advancements in geomorphic studies on the upper Indus basin focusing on recent tectonics (endogenic) are lacking, thus implementing a partial picture of landscape evolution. This article attempts to synthesize geomorphic indices of active tectonics to understand the prevalence of neotectonic activity in the Ladakh area. A combination of geomorphic field data, morphometric analysis and previously published incision rates, denudation rates, the chronology of landform features and soft-sediment deformation structures are used to suggest the region is undergoing differential tectonic activity. Based on morphometric parameters and landform characteristics, the region is divided into three differentially uplifted morphotectonic segments. The neotectonic activity is inferred to be the response to the thrusting of Indus Molasse over the rigid Ladakh Batholith along with oblique convergence of the Indian plate in the study area. This led to the development of a system of back thrust (Stok Thrust) and cross-cutting minor strike-slip faults. Recurrent tectonic activity largely responding to the differential movement along this system of thrust fault is recorded at 50 ka, 35 ka and 21 ka (Last Glacial Maxima) through lower Greenlandian (similar to 11 ka) to middle Northgrippian (similar to 6 ka), while the climatically induced topographic changes are marked between similar to 13 and 12 ka.

The Ladakh Range in the Trans Himalaya houses sub-routes of the Silk route through its passes (La in local language) which may have been the main commercial and cultural passage to connect the central Asia and Tibetan region with the rest of India. A ca 6400-220 cal yr B.P. hydroclimatic record of two lakes viz Tsoltak lake and Yaya Tso near the Chang La and Hor La passes of Ladakh Range is presented here. The overall record (mineral magnetic analysis and microbiota) from the Ladakh range shows wetter conditions ca 6400 cal yr BP consistently declining till similar to 5000 cal yr BP and moderately wet and stable till similar to 4300 cal yr BP, followed by an arid cold phase (similar to 4300-4000 cal yr BP). This precedes two moderately wet phases (ca 4300-3500 cal yr BP and ca 1260-220 cal yr BP) and the peak arid conditions between 3500 and 2860 cal yr B P and 2230-855 cal yr BP, which may have affected the trade activities and had an adverse affect of cultural transitions during these periods across the Ladakh Range on the to and fro movements from this northern sub-route branch. The biotic assemblage is rich in Non Pollen Palynomorphs (76%) with minor amounts of pollens (24%). An improvement in the conditions since 855 cal yr BP and thereafter from 340 to 220 cal yr BP records the onset of the cold arid conditions again in the Ladakh Range. Presently due to contemporary deglaciation the Ladakh Range is becoming ice free and a number of lakes surrounded by herbaceous meadows are seen in the area due to glacial melt, likely to encourage the human settlements to soon occupy the higher reaches that will negatively affect the natural lake productivity.

Nous rapportons de nouvelles donnees geochimiques sur l'âge du zircon U – Pb et la roche entiere des roches intrusives mafiques de Pangin de la fenetre de Siang, dans l'est de l'Himalaya. Ces roches mafiques sont des gabbros a grains moyens a grossiers, constitues principalement de plagioclase et de clinopyroxene avec des phases accessoires (hornblende + Oxydes de Fe – Ti) qui conservent une texture granulaire et imbriquee. Sur le plan geochimique, ils affichent une affinite en basalte enrichi au milieu de la dorsale oceanique (E-MORB) caracterisee par des modeles de REE moderes a legerement fractionnes marques par (La / Yb)_N = 2.65 - 3.99 . Leurs caracteristiques geochimiques suggerent que les magmas parentaux de ces roches ont ete formes par des degres moyens a plus eleves (~12–28%) de fusion partielle similaire a celle du manteau asthenospherique dans la zone de transition grenat-spinelle. Les zircons magmatiques de deux gabbros donnent des âges U – Pb de 521,50 ±2.53 Ma et 568 ±2 Ma. Ce nouvel âge revele deux impulsions de magmatisme mafique neoproterozoique tardif et cambrien precoce qui sont incompatibles avec la distribution temporelle du magmatisme paleozoique dans la fenetre de Siang de l'Himalaya oriental. Cependant, sur la base des resultats de cette etude et de la correlation du magmatisme mafique extensif continental dans le nord-ouest de l'Himalaya, nous suggerons que des roches intrusives mafiques etudiees auraient pu etre generees dans un environnement tectonique extensionnel au cours du cycle orogenique panafricain de longue duree du Neoproterozoique tardif au Cambrien precoce qui s'est termine avec la formation du supercontinent du Gondwana.

We report new U–Pb zircon age and whole-rock geochemical data from the Pangin mafic intrusive rocks of the Siang window, eastern Himalayas. These mafic rocks are medium to coarse-grained gabbros, consisting mainly of plagioclase and clinopyroxene with accessory phases (hornblende $+$ Fe–Ti oxides) that retain granular and interlocking texture. Geochemically, they display enriched-mid oceanic ridge basalt (E-MORB) affinity characterized by moderate to slightly fractionated REE patterns marked by $(\mathrm{La}/\mathrm{Yb})_{\mathrm{N}} = 2.65-3.99$. Their geochemical characteristics suggest that the parental magmas of these rocks were formed by medium to higher degrees (∼12–28%) of partial melting similar to that of the asthenospheric mantle in the garnet-spinel transition zone. Magmatic zircons from two gabbros yield U–Pb ages of 521.50 $\sim $ 2.53 Ma and 568 ${\pm }$ 2 Ma. This new age reveals two pulses of Late Neoproterozoic and Early Cambrian mafic magmatism that are inconsistent with the temporal distribution of Paleozoic magmatism in the Siang window of the Eastern Himalayas. However, based on the results of this study and the correlation of continental extensional mafic magmatism in the Northwest Himalaya, we suggest that investigated mafic intrusive rocks might have been generated in an extensional tectonic environment during the long-lasting Pan-African orogenic cycle of the late Neoproterozoic to early Cambrian which ended with the formation of the Gondwana supercontinent.

Geometry and kinematics of a hitherto ignored crustal scale tectonic discontinuity from the west-central sector of the Himalaya, viz. the North Almora Fault (NAF) is discussed in this paper. Choice of the tectonic model for response of the Himalayan-South Tibetan ensemble to the Tertiary Himalayan continental collision is largely dictated inter alia by the geometry and kinematics of the large orogen parallel strike slip faults in the region. Based on field, laboratory and satellite imagery data, it is concluded that the North Almora Fault/Thrust is not one but two closely parallel tectonic discontinuities viz. (i) the North Almora Fault, a steep south dipping high angle brittle fault with a dominant east slip and subordinate dip slip component and (ii) the North Almora Thrust, a low angle south dipping thrust marking the northern boundary of the large Almora - Jajarkot Nappe. The > 500 km long dextral strike slip North Almora Fault mimicking the similar to 800 km long Karakoram Fault is responsible for significant strain partitioning in the west-central Lesser Himalaya. The North Almora Fault assumes special salience for the Himalayan tectonics as it partitions sizable strains in addition to the Karakoram Fault in the region and lends support to the oblique convergence model that best describes the Himalayan extensional and strike slip deformation.

The chemical and petrological correlation of metamorphic nappes and klippes overlying the Proterozoic sedimentary units in the Kumaun Himalaya is still debated. The Ramgarh and Almora gneisses, not previously distinguished in the Askot Klippe, show distinct field, petrological and chemical signatures markedly similar to the tectonostratigraphic disposition of the Almora Nappe. A negative Eu anomaly in the Ramgarh granitic gneisses indicates lesser plagioclase fractionation while the Eu anomaly in the Almora pelitic gneisses is likely to have been controlled by feldspar crystallization in restites. During the anatexis at > 776°C temperature and >6.6 kbar pressure, the melt moved slightly away to its crystallization sites. The Rb/Sr ratio ∼0.54 and Nb ∼10 ppm is consistent with the granodioritic composition. The negative Sr anomaly in the underlying Ramgarh granitic gneisses indicates a distinct mantle derived source/plagioclase fractionation with a notable correspondence to other late orogenic granites, particularly the basement Ulleri gneisses from the Nepal Himalaya. Ramgarh gneisses plot in the late‐ and post‐COLG field. The Askot ensemble is likely to be the tectonometamorphically reworked basement, viz. the Ramgarh Group along with its metapelitic cover of the Almora Group, together comprising southward thrust remnants of the leading edge of the Indian Plate that collided with Tibet during the Tertiary Himalayan orogeny.

On 04 October 2016, a severe landslide had occurred in the vicinity of Khotila village in Dharchula, region of NE Kumaun Himalaya. This landslide may be classified as typical rockslide, involving thin veneer of debris on the slope as well as the highly shattered rockmass. The slide has been divided into three morpho-dynamic zones, viz., (i) Zone of detachment between elevation 1000 and 960 m, (ii) Zone of transportation between elevation 960 and 910 m, and (iii) Zone of accumulation between elevation 910 and 870 m. The landslide had occurred at the end of the monsoon season when the slope was completely saturated. It has been noted that the area received \({\sim }88\%\) rainfall during the monsoon months which is about two times more rainfall during 2016 monsoon than during 2015 monsoon. Geotechnical testing of the soil overlying the rockmass, corroborate the soil as ‘soft soil’ with compressive strength of 42 kPa and friction angle of \(27.4{^{\circ }}\). Granulometry confirms the soil as having \({>}97\%\) sand and silt size particles and \({<}3\%\) clay size particles, indicating higher permeability. Mineralogically, the soil dominantly constitutes quartz, muscovite and clinochore. Though no swelling clay minerals has been observed, the higher permeability and low strength of the soil, and concentrated higher rainfall during 2016 are the main causes for the landslide to occur. This landslide has partially blocked the flow of Kali river that serve as a boundary between India and Nepal and is endangering the habitants of the Khotila and Bangabagar villages, situated downstream in the Indian and Nepalese side of the Himalaya. In order to understand the stability of the slope, finite element modelling of the landslide has been carried out that points towards higher concentration of stresses in the landslide zone, indicating that there is further probability for the failure of landslide mass. It is therefore suggested that the landslide must be monitored continuously, particularly during the rainy season and also the risk posed by this landslide must be evaluated so as to avoid any further loss to life and infrastructure in the region.