Nagthat Formation: An example of a progradational,tide-dominated Proterozoic succession in Kumaun Lesser Himalaya,India

The Proterozoic Nagthat Formation of the Krol-belt succession, in the Nainital area, is composed mainly of fine- to coarse-grained quartzarenite with a subordinate amount of purple to grey sandstone, siltstone-shale and conglomerate horizons. The association with spilitic lava flows, variable palaeocurrent trends and the restricted lateral extent of the Nagthat Formation within the Krol-belt succession imply an active role for tectonism in the basin of deposition. In the upward coarsening succession of the Nagthat Formation, six major lithofacies have been identified: medium- to coarse-grained gravelly quartzarenite (Lithofacies A), planar cross-bedded, medium-grained quartzarenite (Lithofacies B), horizontally laminated, fine-grained quartzarenite (Lithofacies D), interbedded sandstone-shale (Lithofacies E) and matrix-supported conglomerate (Lithofacies F). The constituent lithofacies are repetitive in nature, forming upward fining unit cycles and interpreted to reflect deposition as upper shore-face, shoals and bars, barrier-beachface, tidal channels (inlets), intertidal–sandflat–mixedflat environments and, occasionally, in the form of gravity flows in subtidal channels. The general upward coarsening succession of the Nagthat Formation represents deposition in a progradational (regressive) barrier island system. The palaeocurrent pattern in the Nagthat Formation is distinctly polymodal and indicates sediment distribution across the roughly NW–SE trending shoreline, in response to a dominating flood tidal current system. The palaeocurrent pattern shows higher variability in the upper shore-face deposits than in the tidalflat domain. A recycled metasedimentary terrain served as the source for the Nagthat Formation, probably supplying the sediments from E, NE and S directions.     

Geothermal evolution of the evaporite-bearing sequences of the Lesser Himalaya, India

Neoproterozoic evaporites occurring in the western part of the Lesser Himalaya in India, coeval to Pakistan, Iran and Oman evaporites, were investigated in order to understand the degree of metamorphism in them and in associated carbonates. The evaporite-bearing succession occurs in association of phyllite, quartzite and carbonate near the Main boundary Thrust. In order to learn the details about the burial history of these evaporite rocks, the Kübler illite crystallinity index (KI) was measured from the illite peaks of the clay minerals separated from the evaporite rocks and it indicated that this section has reached a maximum temperature up to ~300°C. Microthermometric measurements on fluid inclusions present in the associated dolomite show range of homogenization temperatures (Th), from 220 to 280°C, well within the temperature range of anchizone metamorphism. Additionally, dolomite shows a highly negative δ¹⁸O signature (mean, −15.5‰_PDB), which is more likely related to diagenetic overprint from deep burial conditions rather than original precipitation from ¹⁸O-depleted seawater. The evaporites (sulfates and chloride) probably were transformed many times after their precipitation, but they have retained only the features developed during last one or two phases of alteration and deformation as they are continuously susceptible to minor changes in temperatures and stresses. The final temperature range of 42–78°C in sulfates and chloride gives thermal approximation estimate that is not in concordance with the thermal history of the basin and are likely related to conversion of anhydrite into gypsum and recrystallization of halite during exhumation. Highly negative oxygen isotopic composition, homogenization temperatures and KI values equivalent to a high anchizone metamorphism suggest a burial depth of ~10 km for these terminal Neoproterozoic evaporite-bearing sequences of the Lesser Himalaya.     

The application of GIS-based bivariate statistical methods for landslide hazards assessment in the upper Tons river valley,Western Himalaya,India

Landslides are one of the most frequent and common natural hazards in many parts of Himalaya. To reduce the potential risk, the landslide susceptibility maps are one of the first and most important steps in the landslide hazard mitigation. Earth observation satellite and geographical information system-based techniques have been used to derive and analyse various geo-environmental parameters significant to landslide hazards. In this study, a bivariate statistics method was used for spatial modelling of landslide susceptibility zones. For this purpose, thematic layers including landslide inventory, geology, slope angle, slope aspect, geomorphology, slope morphology, drainage density, lineament and land use/land cover were used. A large number of landslide occurrences have been observed in the upper Tons river valley area of Western Himalaya. The result has been used to spatially classify the study area into zones of very high, high, moderate, low and very low landslide susceptibility zones. About 72% of active landslides have been observed to occur in very high and high hazard zones. The result of the analysis was verified using the landslide location data. The validation result shows significant agreement between the susceptibility map and landslide location. The result can be used to reduce landslide hazards by proper planning.     

Geochemistry and petrogenesis of the Palampur metavolcanics, Lesser Himachal Himalaya, India

Summary The Palampur metavolcanics (PV) in the northwest Himalaya are part of the Late Archaean (2.5 Ga) Rampur flood basalt province (RFBP) which represents one of the oldest manifestation of worldwide mafic magmatism. The volcanics occur as mafic lava flows with evidence of two phases of deformation. The first phase resulted in recrystallisation which almost completely obliterated the primary mineralogy, and the second phase was of weak cataclasis. Immobile trace element ratios as well as cation percent Al - (Fe - Ti) - Mg indicate that the volcanics are tholeiitic in composition. The chemical characteristics, such as the decoupling between HFS and LIL elements i.e., distinct negative Sr, Nb and Ti anomalies in the double normalisation ratios spiderdiagram together with low Ti/Y and Zr/Y ratios, testify the rocks as low-Ti continental flood basalts. The chemical variations in the volcanics can be related to varying extents of partial melting of the mantle source(s), followed by fractional crystallisation (predominantly olivine and clinopyroxene over plagioclase). Positive correlation between LREE and Fe abundances, Ce-Nd and Y/Nd-Zr/Y data preclude any significant role of crustal contamination in the evolution of their bulk chemistry. The REE data and [Mg]-[Fe] relations rather suggest that the parental magma of the PV derived from non-pyrolitic source(s) which was heterogeneous with respect to enrichment in Zr, LREE and Fe/Mg ratios. Mantle metasomatism appears to be the main process of such source enrichment, possibly caused by the addition of a volatilerich silicate melt phase.[/ p]

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Geochemie und Petrogenese der Palampur Metavulkanite, Lesser Himachal Himalaya, Indien

Zusammenfassung Die Palampur Metavulkanite (PV), im nordwestlichen Himalaya, gehören zur spätarchaiischen (2.5 Ga) Rampur Plateau-Basalt-Provinz (RFBP), die einen der ältesten, weltweiten Phasen von mafischem Magmatismus manifestiert. Die Vulkanite treten als mafische Lavaströme auf und zeigen zwei Phasen von Deformation. Die erste resultierte in einer Rekristallisation, die nahezu den gesamten primären Mineralbestand überprägt hat. Die zweite Phase ist durch schwache Kataklase repräsentiert. Immobile Spurenelementverhältnisse, wie auch die Kationenprozent von Al- (Fe- (-Ti) -Mg, deuten eine tholeiitische Zusammensetzung der Vulkanite an. Die chemischen Charakteristika, die im unterschiedlichen Verhalten der HFS und LIL Elemente deutlich werden, deutlich negative Sr, Nb und Ti Anomalien in den zweifach normalisierten Spiderdiagrammen, niedrige Ti/Y und Zr/Y Verhältnisse, bezeugen, dass es sich um Ti-arme, kontinentale Plateaubasalte handelt. Die chemischen Unterschiede innerhalb der Vulkanite können auf unterschiedliche Grade von Aufschmelzung des (der) Mantelmaterials(e), gefolgt von fraktionierter Kristallisation (vor allem Olivin und Klinopyroxen, untergeordnet Plagioklas), zurückgeführt werden. Positive Korrelation der LREE mit Fe, wie auch die Ce-Nd und Y/Nd-Zr/Y Daten schließen eine signifikante Rolle von Krustenkontamination in der Evolution der Gesteinschemie aus. Die REE Daten und die /Mg/-/Fe/ Verhältnisse lassen eher vermuten, dass das Ausgangsmagma der PV von einem nicht-pyrolitischen Material stammt, welches bezüglich Anreicherung an Zr, LREE und Fe/Mg Verhältnis heterogen gewesen ist. Mantelmetasomatose scheint der Hauptprozeß für diese Anreicherng des Ausgangsmaterials gewesen zu sein, die möglicherweise durch Zufuhr einer silikatischen Schmelzphase, reich an flüchtigen Bestandteilen, hervorgerufen wurde.[/ p]

     

Deformation mechanisms in the frontal Lesser Himalayan Duplex in Sikkim Himalaya,India

Understanding deformation mechanisms in Himalayan rocks is a challenging proposition due to the complex nature of the deformed rocks and their genesis. Crustal deformation in the Himalayan thrust belt typically occurs in elastico-frictional (EF) or quasi-plastic (QP) regimes at depths controlled mainly by regional strain-rate and geothermal gradient. However, material property, grain-size and their progressive changes during deformation are also important controlling factors. We present evidence of EF deformation from Gondwana rocks developed during the emplacement of one of the frontal horses (Jorthang horse) in the Lesser Himalayan Duplex (LHD) structure associated with Lesser Himalayan rocks in the footwall of the Ramgarh thrust in the Rangit window near Jorthang in the Sikkim Himalaya. The rocks in the horse exhibit systematic changes in microand meso-structures from an undeformed protolith to cataclasite suggesting that it was emplaced under elastico-frictional conditions. Meso- to micro-scale shear fractures are seen developed in Gondwana sandstone and slate while intercalated fine-grained shale-coal-carbonates are deformed by cataclastic flow suggesting that material property and grain-size have played an important role in the deformation of the Jorthang horse. In contrast, the hanging wall schists and quartzites of the Ramgarh thrust exhibit quasi-plastic deformation structures. This suggests that the Jorthang horse was emplaced under shallower crustal conditions than the antiformally folded Ramgarh thrust sheet even though the Ramgarh sheet presently overlies the Jorthang horse.     

Normal faults in Panjal Thrust Zone in Lesser Himalaya and between the Higher Himalaya Crystallines and Chamba sequence in Kashmir Himalaya,India

Normal faults on mesoscopic scale are observed in the Panjal Thrust Zone in the Dalhousie area of western Htmachal. The boundary between the southern margin of the Higher Himalaya Crystalline (HHC) of Zanskar and the Chamba syncline sequence is also described as a normal fault, referred to as Bhadarwah Normal Fault in the Bhadarwah area of Doda district on the basis of field mapping and shear sense criteria using S-C fabric and porphyroblast rotation. The occurrence of these normal faults suggests that the extensional tectonic regime was not restricted only to the Zanskar shear zone area but that it also occurs south of the Higher Himalayan range. This suggests NE-directed subhorizontal extension and exhumation of deeper level rocks of Higher Himalaya Crystallines.     

Petrography,geochemistry and regional significance of crystalline klippen in the Garhwal Lesser Himalaya,India

Uphalda gneisses (UG) is a crystalline klippe located near Srinagar in Garhwal Himalaya. These gneisses are compared with Debguru porphyroids (DP) (≈Ramgarh group) of Garhwal–Kumaun Himalaya and Baragaon mylonitic gneisses (BMG) of Himachal Himalaya. Petrographic study reveals that the deformation of UG was initiated at higher temperature (above 350°C) and continued till lowering of temperature and deformation led to the mylonitization.     

Modification of fold geometry in Almora Crystalline Shear Zone,Lesser Himalaya,India

The folds generally initiate at several discrete points along a layer or multilayer undergoing compressional forces. These compressional forces often lead to rotation of fold segments and in all such regimes, folds are strongly asymmetrical and are in complete agreement with the direction in which the force is applied and also with the related thrust sheet movement. This paper illustrates the progressive change in fold geometry with increasing compression and ductile shearing using natural example as studied in the Almora Crystalline Zone (ACZ).     

Structure and petrology of mylonite and related rocks from the Lesser Himalaya,Garhwal, India

In the Lesser Himalayan region of Garhwal, an elongate, NW-SE trending zone of mylonitic rocks is developed along the Singuni Thrust within the metasedimentary formation of the Deoban-Tejam Belt. Detailed petrography of various mylonitic rocks indicates that a quartz and felspar porphyry was emplaced along the Singuni Thrust. This was initially metamorphosed in the almandine-amphibolite facies before profound ruptural or cataclastic and crystalloblastic deformation evolved mylonitic rocks in the green schist facies. Southwesterly dipping foliation and an equally prominent mica lineation plunging in the same direction are developed in these mylonitic rocks. The quartzite is also intensely cataclastically deformed in the green schist facies and is highly schistose with a prominent mica lineation normal to the trace of Singuni Thrust, Uttarkashi Thrust and Main Central Thrust in the ‘a’ direction of tectonic transport. In quartzite and mylonitic rocks, a probable contemporaneous development of the metamorphic and structural elements has been postulated along the Singuni Thrust during large scale tectonic movements. Normally exposed Gamri Quartzite is more metamorphosed near its base along the Singuni Thrust and Uttarkashi Thrust while the intensity of deformation increases near the top of normally exposed quartzite along the Main Central Thrust and, thus, signifying the role of thrusting in cataclastically deforming the rocks and contributing to the phenomenon of widespread reversal of metamorphism in the Lesser Himalaya.     

Seismic hazard and probability assessment of Kashmir valley,northwest Himalaya,India

Seismic hazard analysis of the northwest Himalayan belt was carried out by using extreme value theory (EVT). The rate of seismicity (a value) and recurrence intervals with the given earthquake magnitude (b value) was calculated from the observed data using Gutenberg–Richter Law. The statistical evaluation of 12,125 events from 1902 to 2017 shows the increasing trend in their inter-arrival times. The frequency–magnitude relation exhibits a linear downslope trend with negative slope of 0.8277 and positive intercept of 4.6977. The empirical results showed that the annual risk probability of high magnitude earthquake M?≥?7.7 in 50 years is 88% with recurrence period of 47 years, probability of M?≤?7.5 in 50 years is 97% with recurrence period of 27 years, and probability of M?≤?6.5 in 50 years is 100% with recurrence period of 4 years. Kashmir valley, located in the NW Himalaya, encompasses a peculiar tectonic and structural setup. The patterns of the present and historical seismicity records of the valley suggest a long-term strain accumulation along NNW and SSE extensions with the decline in the seismic gap, posing a potential threat of earthquakes in the future. The Kashmir valley is characterized by the typical lithological, tectono-geomorphic, geotechnical, hydrogeological and socioeconomic settings that augment the earthquake vulnerability associated with the seismicity of the region. The cumulative impact of the various influencing parameters therefore exacerbates the seismic hazard risk of the valley to future earthquake events.     

Stratigraphy and provenance of Late Palaeozoic diamictites in parts of Garhwal Lesser Himalaya,India

The Garhwal Lesser Himalayan Krol Belt contains two well developed diamictite horizons in the Late Palaeozoic Blaini Formation. Structureless and massive diamictites contain clasts of different shape, roundness and lithologies comprising mainly shale, slate, phyllite, quartzite, vein quartz and limestone dispersed in fine sandy argillaceous and calcareous matrix.Clast composition and petrography of the diamictites and other lithologies of the Blaini Formation reveal the presence of sedimentary and low grade metamorphic rocks in the provenance of the Blaini. The provenance seems to be the Lesser Himalayan terrain of the Simla Slate, Jaunsar and Shali-Deoban carbonates which had probably undergone structural deformation prior to the Late Palaeozoic. Two glacier advances deposited the diamictites near the shoreline of the Krol Basin during Late Palaeozoic.

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Zusammenfassung Im Krol Belt des Kleinen Himalaya sind in der jungpaläozoischen Blaini-Formation zwei Horizonte mit sedimentären Diamictiten enthalten. Die strukturlosen und massiven Diamictite enthalten Klastika verschiedener Form, Rundung und Lithologie. So findet man Schiefer, Phyllite, Quarzite, Gangquarze und Kalke in einer feinsandigen, tonigen Matrix mit Karbonatanteilen. Die Zusammensetzung der Klaste und die Petrographie der Diamictite sowie der übrigen Gesteine der Blaini-Formation zeigen die Anwesenheit von Sedimentgesteinen und schwach metamorphisierten Gesteinen im Einzugsbereich der Blaini-Formation. Dieser Bereich kann die Simla-Schiefer und die Jaunsar- und Shali-Deoban-Karbonate des Kleinen Himalaya mit umfassen, die vermutlich vorjungpaläozoisch metamorphisiert wurden. Während zweier Gletschervorstöße sind die Diamictite randlich im Krol-Becken während des Jungpaläozoikums abgelagert worden.

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Résumé Dans la ceinture de Krol de l'Himalaya mineur, la Formation de Blaini, d'âge Paléozoique supérieur, renferme deux horizons à diamictites sédimentaires. Celles-ci, massives et sans structure interne, contiennent des éléments clastiques de forme arrondi et lithologie différents; ce sont des schistes métamorphiques, des phyllites, des quartzites, du quartz-filonien et des calcaires disposés dans une matrice fine, argilosableuse avec participation carbonatée. La composition des éléments clastiques et la pétrographie des diamictites, comme celles des autres roches de la Formation de Blaini, montrent la présence de roches sédimentaires et de roches faiblement métamorphiques de même provenance que la formation de Blaini; cette provenance peut comprendre les schistes de Simla et les roches carbonatées de Jaunsar et de Shali-Deoban qui furent métamorphisées probablement avant le Paléozoique supérieur. C'est au cours de deux avancées glaciaires que les diamictites ont été déposées en bordure du bassin de Krol pendant le Paléozoique supérieur.

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Tracing ionic sources and geochemical evolution of groundwater in the Intermountain Una basin in outer NW Himalaya,Himachal Pradesh,India

The present research aims to identify sources of ions and factors controlling the geochemical evolution of groundwater in an intermountain basin, comprising hill and valley fill region, of Outer Himalaya in Himachal Pradesh, India. The groundwater samples collected from 81 tubewells and handpumps are analyzed for major ions, trace metals and stable isotopes (δ¹⁸O and δD). Geochemically the dominant hydrochemical facies in the Una basin are Ca–HCO₃, Ca–Mg–HCO₃ and Na–Cl types at few locations. A relatively lower ionic concentration in the valley fills indicates dilution and low residence time of water to interact with the aquifer mass due to high porosity and permeability. The ionic ratios of 0.9, 0.8 and 3.8 to 5.7, respectively, for (Ca?+?Mg): HCO₃, (Ca?+?Mg): (HCO₃?+?SO₄) and Na: Cl, suggests that ionic composition of groundwater is mainly controlled by rock weathering of, particularly by dissolution/precipitation of calcrete and calcite hosted in rock veins and Ca–Na feldspar hosted in conglomerate deposits derived from the Higher and Lesser Himalaya during the formation of Siwalik rocks. Although Na, K, NO₃ and SO₄ are introduced in the groundwater through agricultural practices, Na has also been introduced through ion exchange processes that have occurred during water–rock interaction, as indicated by negative CAI values. Factor analysis further suggests three major factors affecting the water chemistry of the area. The first two factors are associated with rock weathering while the third is anthropogenic processes associated with high nitrate and iron concentration. High concentrations of Fe and Mn ions that are exceeded that of WHO and BIS standards are also present at few locations. The recharge of groundwater in the Outer Himalaya is entirely through Indian Southwest Monsoon (ISM) and depleted ratios of δ¹⁸O/δD in valley region indicate infiltration from irrigation in recharging the groundwater and fractionation of isotopes of precipitation due to evaporation before infiltration. High d-excess values and inverse relation with δ¹⁸O are indicative of secondary evaporation of precipitation during recharge of groundwater.     

Chemodynamics of trace metal fractions in surface sediments of the Pandoh Lake,Lesser Himalaya,India

The seasonal variation in the trace metals’ concentrations (Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were investigated in surface sediments of the Pandoh Lake. The horizontal distribution of TC, TN, and TP reflects spatial and temporal differences in sedimentary organic production. The chemical sequential extraction of heavy metals was carried out by seven-step fractionation scheme (Leleyter and Probst in Int J Environ Chem 73:109–128, 1999). The significant concentrations of Ni and Cd were associated with “water soluble (Eua)” fraction in the monsoon and winter, respectively, while “exchangeable (Exch)” and “carbonate-bound (Carb)” fractions for Ni and Cd were abundant in winter and summer. The Cd, Cu, and Pb associated with “Exch” fraction in the summer season support their availability on exchange sites due to oxidized nature of surface sediments. Enrichment of Co, Fe, Mn, and Zn in “AFeO” fraction showed poor bioavailability, while Cd, Cu, and Mn in the monsoon, Co in the winter and summer, and Zn in the winter season showed significant “organically bound (Org)” fraction. The ANOVA was significant for chemical fractions of trace elements except “Carb” fraction of Pb and Zn and “CFeO” fraction of Pb. Factor analysis revealed that the “Eua”, “Exch”, and “Carb” fractions together control the metal enrichment of “MnO”, “AFeO”, and “CFeO” fractions in the summer season.     

Phosphorus fractionation in surficial sediments of Pandoh Lake,Lesser Himalaya,Himachal Pradesh,India

The fractionation of P in Pandoh Lake surface sediments has been investigated for the first time in order to understand its environmental availability and sources, and the eutrophication status of this lake. Inorganic-P is present mainly as authigenic-P (step-III). The authigenic P concentration is higher in winter relative to the summer and monsoon seasons and ranged from 35.9 to 46.9 μg/g. The loosely sorbed or exchangeable-P (step-I), Fe(III)-bound-P (step-II) and detrital inorganic-P (step-IV) were higher in the monsoon season and varied from 3.70 to 11.1 μg/g, 16.9 to 32.0 μg/g and 9.89 to 17.0 μg/g, respectively. Organic-P reached a maximum in the summer season and ranged from 8.00 to 14.9 μg/g. Authigenic-P and detrital inorganic-P show seasonal changes, as pH influences the interaction between P and CaCO₃ in the water column. In the winter season, phosphate is precipitated out of the water column and fixed in the sediments as a result of an increase in pH. Calcite-bound-P in the sediments may be redissolved by decreasing pH in the summer season. Relatively high rates of mineralization during the monsoon results in the seasonal pattern of organic-P fractionation to sediment as follows: monsoon = winter < summer. Iron, Ca, organic matter and silt and clay contents seem to play a significant role in regulating the seasonal P budget. Principal component analysis (PCA) was used to identify the factors which influence sedimentary P in the different seasons.     

The role of fluids in the formation of talc deposits of Rema area,Kumaun Lesser Himalaya

Talc deposits of Rema area in the Kumaun Inner Lesser Himalaya are hosted within high magnesium carbonates of the Proterozoic Deoban Formation. These deposits occur as irregular patches or pockets mainly within magnesite bodies, along with impurities of magnesite, dolomite and clinochlore. Textures represent different phases of reactions between magnesite and silica to produce talc. Petrography, XRD and geochemistry reveal that the talc has primarily developed at the expense of magnesite and silica, leaving dolomite largely un-reacted. Early fluid inclusions in magnesite and dolomite associated with talc are filled with H₂O+NaCl+KCl ± MgCl₂ ± CaCl₂ fluids, which represent basin fluid system during diagenesis of carbonates. Their varied degree of re-equilibration was although not pervasive but points to increased burial, and hence requires careful interpretation. H₂O-CO₂ fluid with XCO₂ between 0.06 and 0.12 was equilibrated with talc formation. The reaction dolomite+quartz → talc was not extensive because T-X_CO2 was not favourable, and talc was developed principally after magnesite+quartz.     

Active tectonic influence on the evolution of drainage and landscape: Geomorphic signatures from frontal and hinterland areas along the Northwestern Himalaya, India

The Kangra Re-entrant in the NW Himalaya is one of the most seismically active regions, falling into Seismic Zone V along the Himalaya. In 1905 the area experienced one of the great Himalayan earthquakes with magnitude 7.8. The frontal fault system – the Himalayan Frontal Thrust (HFT) associated with the foreland fold – Janauri Anticline, along with other major as well as secondary hinterland thrust faults, provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region. The present study suggests that the flat-uplifted surface in the central portion of the Janauri Anticline represents the paleo-exit of the Sutlej River. It is suggested that initially when the tectonic activity propagated southward along the HFT the Janauri Anticline grew along two separate fault segments (north and south faults), the gap between these two fault and the related folds allowed the Sutlej River to flow across this area. Later, the radial propagation of the faults towards each other resulted in an interaction of the fault tips, which caused the rapid uplift of the area. Rapid uplift resulted in the disruption and longitudinal deflection of the Sutlej river channel. Fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past. Geomorphic signatures, like the sharp mountain fronts along the HFT in some places, as well as along various hinterland subordinate faults like the Nalagarh Thrust (NaT), the Barsar Thrust (BaT) and the Jawalamukhi Thrust (JMT); the change in the channel pattern, marked by a tight incised meander of the Beas channel upstream of the JMT indicate active tectonic movements in the area. The prominent V-shaped valleys of the Beas and Sutlej rivers, flowing across the thrust fronts, with Vf values ranging from <1.0–1.5 are also suggestive of ongoing tectonic activity along major and hinterland faults. This suggests that not only is the HFT system active, but also the other major and secondary hinterland faults, viz. the MBT, MCT, SnT, NaT, BaT, and the JMT can be shown to have undergone recent tectonic displacement.     

Geochemical Characteristics of Proterozoic Mafic Dykes from the Bomdila Group of Rocks,NE Lesser Himalaya,India

正The mafic dykes from the Paleoproterozoic Bomdila Group of metasedimentary rocks,Arunachal Pradesh,NE Lesser Himalaya,India have been analyzed for major and trace elements geochemistry essentially to understand their     

Back-thrusting in Lesser Himalaya: Evidences from magnetic fabric studies in parts of Almora crystalline zone,Kumaun Lesser Himalaya

The present study aims to understand evolution of the Lesser Himalaya, which consists of (meta) sedimentary and crystalline rocks. Field studies, microscopic and rock magnetic investigations have been carried out on the rocks near the South Almora Thrust (SAT) and the North Almora Thrust (NAT), which separates the Almora Crystalline Zone (ACZ) from the Lesser Himalayan sequences (LHS). The results show that along the South Almora Thrust, the deformation is persistent; however, near the NAT deformation pattern is complex and implies overprinting of original shear sense by a younger deformational event. We attribute this overprinting to late stage back-thrusting along NAT, active after the emplacement of ACZ. During this late stage back-thrusting, rocks of the ACZ and LHS were coupled. Back-thrusts originated below the Lesser Himalayan rocks, probably from the Main Boundary Thrust, and propagated across the sedimentary and crystalline rocks. This study provides new results from multiple investigations, and enhances our understanding of the evolution of the ACZ.