NE Himalaya Research Articles

Deciphering Hydrochemistry and Fluid-Mineral Equilibria from Characteristic Low-Enthalpy Geothermal Waters of Himalaya and Eastern India

Geothermal energy, with associated low-carbon emissions compared to conventional fossil fuels, is presently one of the potential renewable energy sources. The decryption of the chemistry of thermal manifestations of geothermal systems, in terms of relative abundances of various chemical facies, is mandatory before launching systematic geothermal exploration in a given area as it provides valuable information on the basic characteristics of the geothermal reservoir. For the present study, three clusters of hot springs have been selected -1) Shyok-Nubra valleys geothermal prospect in NW Himalaya, 2) Subansiri valley geothermal areas in NE Himalaya and 3) the hot spring system occurring along Munger-Saharsa Ridge Fault Zone (MSRF) in the Eastern part of India. The study of these geothermal systems with low to moderately high temperatures of 35−75°C, has been carried out with two main objectives. The first objective is to estimate reservoir temperature and other characteristics in the three above-mentioned hot spring groups using conventional chemical geothermometry techniques for the first-hand assessment of the quality of the geothermal resource and postulating its possible application. The second objective of the study is to understand the distribution of stable isotopes (δ2H and δ18O) in the studied geothermal systems to reveal reservoir-related hydrological aspects of the geothermal system. The three groups of hot springs show large variations in total dissolved solids (TDS) from <150 to about 1800 mg/L. Enigmatic and inexplicably low TDS values of 126 to 150 mg/Lare reported from the three Bhimband hot springs along MSRF Zone. These springs discharge Ca−Mg−HCO3 type water. The dearth of dissolved ionic species in these springs indicates lack of water-rock interaction in Bhimband area. Silica is the most abundant solute species and corresponds to a reservoir temperature of about 75°C. It may be inferred that relatively inert lithology in the reservoir and very high water-to-rock ratio might have rendered the observed chemical signatures to Bhimband hot springs. Shyok-Nubra springs at Changlung and Panamik are predominantly Na-HCO3 type with TDS values of about 1700 and 550 mg/L, respectively. These hot springs give an indication of water-rock interaction in different types of lithology at temperatures of 120 to >150°C resulting in the observed chemical differences between the two. Thermal water at Taksing in NE Himalaya is also Na−HCO3 type. Chetu hot spring with TDS of >1100 mg/Lis anomalous in two ways. First, it has a very high SO4 content of 358 mg/Land second, it has the lowest silica value. There is a possibility that the Chetu hot spring has its chemistry influenced by the dissolution of sulfates of Ca and Na. Preliminary stable isotope study indicates that the geothermal fluid is derived from meteoric sources. The lack of any indication for positive δ18O-shift suggests that reservoir temperatures of the springs are generally low. Keywords: Thermal Waters, Hydrogeochemistry, Reservoir Temperature, Stable Isotopes, Himalayas, Bihar

Signatures of 16th and 19th centuries paleo-earthquakes along the Himalayan Frontal Thrust (HFT), NW Himalaya, India: Implications to seismic hazard assessment

The Himalayas, one of the most seismically active regions in the world, experienced several damaging earthquakes in the recent past. Historical data (limited) and paleoseismic studies indicate that some portions of the Himalayas did not rupture during the historic time and have the potential to host major earthquakes. The paleoseismic study was conducted in the mesoseismal zone of the 1905 (Mw7.8) Kangra earthquake, NW Himalaya. Two trenches (ABT1 and ABT2) excavated across the Hajipur Fault (HF2) – an imbricated fault of Himalayan Frontal Thrust (HFT) near Asparbadaliya revealed signatures of at least three paleo-earthquakes, displacing/deforming young Quaternary deposits along NE dipping thrust fault strands (F1 and F2). Exposed stratigraphy in trenches and Optically Stimulated Luminescence (OSL) calibrated/modeled ages suggest that Event I occurred at around BCE 50 - CE 400; Event II was during CE 1450–1670 and Event III at around CE 1720–1840. A larger interval of ∼900–1000 years between Event-I and Event-II suggests that Event-II was a great earthquake with 8.0 ≥ Mw ≤ 8.5 – correlated with CE 1555 earthquake reported from Kashmir with a rupture length of ∼400–450 km, extending from Kashmir to Chandigarh. Event-III that occurred with an interval of 200–300 years was a large earthquake with a magnitude 7.5 ≥ Mw ≤ 8.0, and a rupture length of ∼200–250 km. We propose that the irregular recurrence interval could be attributed to variation in the distribution of fault system between HFT and Main Central Thrust (MCT) in NW (∼100 km) and Central as well as NE Himalaya (∼40–50 km), suggesting heterogeneity exists along the arc.

Hydroclimatic variability in Northeast India during the last two millennia: Sedimentological and geochemical record from Shilloi Lake, Nagaland

The evolution of the monsoonal climate in the Indian Himalayan region remains poorly understood due to the sparse coverage of paleoclimatic datasets. In the present paper, elemental concentrations and grain size parameters are measured for a radiocarbon-dated sediment core retrieved from Shilloi Lake (Nagaland, India) to understand climate variability over north-eastern India during the past two thousand years. The end-member modeling of grain-size distribution along with the elemental composition and ratios (Mg/Al, Sr/Al, Ti/Al) are used to identify changes in clastic input and authigenic carbonate precipitation as well as lake level changes. In addition, the REE distribution pattern and elemental ratios (U/Th, Europium anomaly – Eu*) are evaluated to understand provenance and redox conditions. We identify two main hydrological events: (i) wet conditions during ~1900 to ~1000 cal yrs. BP characterised by high clastic sediment input (as indicated by increased Mg, Al, Mg/Al) and dominant contribution of fine-grained sediments as represented by end member (EM) 1 in zone 1, and (ii) an increase in aridity as signified by decreasing detrital content and increased coarse-grained sediments (EM3) in zone 2 (~1000 cal yrs. BP to present). The regional comparison of paleoclimatic records from NE Himalaya and central India shows an opposing trend in precipitation patterns. However, a synthesis of hydrological proxy records from the tropical Pacific region does not point to an active role of ENSO in the study region. Comparative analysis of modern precipitation data and paleo-records shows that the opposing behaviour resembles an “active-break” pattern that produces an east-west precipitation dipole in central and northeast India.

A Fragment of Argoland From East Gondwana in the NE Himalaya

AbstractPrevious studies concluded that a Trans‐Tethyan oceanic subduction zone existed prior to Paleogene India‐Eurasia collision, when the ocean lacked intervening continental slivers. In this paper, we present the first report of Early Cretaceous shortening and 152.8 Ma alkali magmatism in the continental sliver Longzi block, a ca. 750 km E‐W by ca. 130 km N‐S tract of the NE Himalaya within the Himalaya orogen. The Longzi block contains overturned south‐vergent folds in Triassic‐Lower Cretaceous strata intruded by 136–123 Ma mafic‐dioritic‐dacite dikes, which constrain the time of Early Cretaceous shortening. Triassic strata with NW Australian affinity and Late Jurassic conglomerates derived from northern India record the pre‐rift history. Evidence for the rifting includes 152.8–145 Ma alkali intrusive rocks, a Late Jurassic unconformity, rapid changes in sediment thickness, and the water depth during deposition of Upper Jurassic strata. The rifting event was coeval with the formation of 152–155 Ma oceanic crust in the NE Indian Ocean and of a Late Jurassic submarine escarpment with 1,200 m of sediments offshore of NW Australia. These data show that the Longzi block was part of westernmost Argoland, a continental sliver that rifted from East Gondwana. The Longzi block subsequently collided with a N‐dipping Trans‐Tethyan intra‐oceanic subduction zone in the Early Cretaceous to generate the relevant shortening, long before the Paleocene continent‐continent collision along the Yarlung‐Tsangpo suture zone. This rift‐collision in the Himalayan region reflects the Mesozoic archipelagic paleogeography in eastern Neotethys, which was preceded by ocean closure, and the two‐stage collision of India‐Eurasia in the Cenozoic.

Earthquake Swarm and Quiescence Precursory to the NE Himalaya 2011 Sikkim Earthquake (M 6.9)

Abstract The September 18, 2011 earthquake of M 6.9 has been critically examined and found to be associated with episodes of precursory swarms, quiescence, mainshock and aftershocks. This earthquake was clearly preceded by precursory swarm activity for almost one year followed by quiescence for one year. The precursory swarm and quiescence period consists of four earthquake swarms and one foreshock event of magnitude (mb ≥ 4.5) in the epicenter preparatory zone of the 2011 Sikkim earthquake. The 2011 Sikkim earthquake recorded about five aftershocks of magnitude (mb) ≥ 4.5 between 2011 and 2014 for the same region. This study shows that the 2011 Sikkim earthquake followed the same sequence of activities as observed for other major earthquakes in the northeast Himalaya.

Crustal Melting Evidence in Migmatites of Higher Himalayan Crystallines (HHC) along Bhagirathi, Dhauliganga Valleys, and Sikkim Himalaya, India

Abstract An attempt has been made to evaluate crustal melting evidence through textural studies within a narrow zone of migmatite present in NW Himalaya along Bhagirathi and Dhauliganga valleys and two zones close to MCT and throughout within in the Sikkim Himalayas, NE Himalaya. It appears that partial melting was initiated by muscovite dehydration melting with a positive volume change driving melt segregation and discontinuous crystallization of peritectic biotite in the leucosome. Further, during retrogression due to cooling, a certain amount of melt was consumed. The occurrence of isolated pseudomorphosed melt pockets and lack of euhedral magmatic flow textured feldspar further indicates that the melt fraction was low for the alignment of crystals. The processes of melt segregation and migration could have been limited. The migmatite leucosomes and a small volume of in situ tourmaline-bearing leucogranite along extensional crenulation cleavages and melt pods indicate water-saturated melting of pelitic metasedimentary rocks. The formation of migmatites happened at around 46 Ma, corresponding to a peak metamorphic event due to collisional tectonics of the Himalayan orogeny. The presence of feeder dikes for main tourmaline-bearing leucogranite indicates that the source for the main body could be migmatite which is also supported by the similarity in REE patterns of the main body and in situ tourmaline-bearing leucogranite.

Mio-Pliocene Tectonics and Exhumation Histories of the NW– and NE–Himalaya

Mio-Pliocene Tectonics and Exhumation Histories of the NW– and NE–Himalaya

Mitigation and Bioengineering Measures for Prevention of the Surbhi Resort Landslide, Mussoorie Hills, Uttarakhand Lesser Himalaya, India

Recent cloud bursts and Glacial Lake Outburst Flood ( GLOF ) in the Uttarakhand Himalaya have triggered catastrophic landslides. Heavy monsoon precipitation lashed Uttarakhand causing devastation and series of new landslides in the region. The Surbhi Resort Landslide is located near the hill station of Mussoorie in Garhwal Himalaya, India, in the Upper Krol Limestone. After intense rain in August 1998, the Krol sedimentary deposits suddenly gave way as a deep-seated landslide, blocking the main Mussoorie-Kemptyartery for 15 days. In 2005, the velocity of the slide was determined to be 4–14 mm/year by previous workers, thus it was still active with a modest intensity. Recently in 2018, during monsoon there was heavy rainfall in the Mussoorie and mud flow in the Kemty Fall area. Huge amounts of quaternary debris are still lying on the slope, another high intensity rainfall or cloud burst in future could trigger another large-scale failure. Based on our recent detailed investigations, following mitigation and bioengineering measures are suggested. To lower the ground water table, a series of horizontal drains should be installed at the base of the crown portion of the slide. This would generate an additional discharge which has to be channeled down Rangaon-ka-Khala, the natural channel, down the slope to the Aglar River flowing in the valley below. To prevent further surface erosion, it is suggested that the Rangaon-ka-Khalamust be bioengineered with shrubs and grasses such as Eriophorum comosum, Saccharum spontanum, Pogonatherum spp. And Wood fordia fruticosa while the surrounding slope must be reforested with Quercus leucotrichophora, Alnus napelensis , Pinus spp.and Cedrus spp. Check dams must be constructed on the entire 3.5 km stretch of the Rangaon-ka-khala to lower the velocity of thewater. This could be done either as gabions or in the form of live fascines of Salix tetrasperma or Dalbergia sissoo. The catchmentarea above the Mussoorie-Kempty road can be expected to collect 60,000 m3 in 24 hours in a 25-years reoccurrence cloud burst. Thus proper drains (0.40 m in dia.) on the inside of the road must be installed. The flow velocity at these extreme events would be 4.8 m/switch is slightly above the recommended value. If this water is allowed to flow down the Rangaon-ka-Khala it will most certainly lead to a major debris slide with a vertical velocity of almost 100 m/s with huge erosive power. For this reason, this discharge should be channeled down in plastic or cement lined pipes, preferably to the west of the Siyagaon Village which is reported as stable rather than in the landslide zone itself. It is concluded that these mitigation measures and bioengineering plantation would certainly help stabilize the Surbhi landslide area to prevent further disaster in future that destroyed the water mills, fields of the surrounding villages and mud flow in popular Kempty Fall area. These measures may also be applicable for the other active landslide zones in the NW(Jammu and Kashmir) and NE ( Darjiling-Sikkim ) Himalaya.

U-Pb zircon ages and Sm-Nd isotopic characteristics of the Lesser and Great Himalayan sequences, Uttarakhand Himalaya, and their regional tectonic implications

Detrital zircons (DZ) and Nd isotopic characteristics constraint maximum depositional ages of two distinct Paleoproterozoic and Neoproterozoic terranes across the Main Central Thrust zone (Munsiari Group) in the Himalaya. New DZ ages and Nd isotopic characters are reported from the Inner Lesser Himalaya (iLH) sedimentary belt (Berinag Group quartzite) and the Munsiari Group through the Great Himalayan Sequence (GHS–Vaikrita Group) across the MCT to the lower parts of the Tethyan Himalayan Sequence (THS) along the Alaknanda–Dhauli Ganga valleys, Uttarakhand Himalaya. The iLH Berinag Group quartzite yielded nearly unimodal DZ U-Pb ages between 2.05 and 1.80 Ga with εNd(0) values of −17 and −23, while the overthrust Munsiari Group, bounded by the Munsiari Thrust at the base and the Vaikrita Thrust (MCT) at the top, represents the Proterozoic magmatic arc with ∼1.95 and 1.89 Ga U-Pb zircon age population with an average of −25 εNd(0) value; the arc developed during the Columbia Supercontinent assembly. In contrast, overthrust Great Himalayan Sequence (GHS–Vaikrita Group) above the MCT is characterized by entirely new Neoproterozoic 1.05–0.85 Ga zircon population, which appears for the first time in this sequence, and has higher εNd(0) values (average −16). Tectonically overlying the GHS, the Tethyan Himalayan Sequence (THS) has first appearance of the Early Paleozoic detrital zircons, with its εNd(0) values like the GHS. Broadly, these characters persist throughout the Himalayan belt from Himachal to NE Himalaya. The iLH sediments were possibly derived from northernly ∼1.9 Ga magmatic arc, and southern the Archean–Proterozoic Aravalli–Bundelkhand nuclei of the Indian craton. Potential sources for the GHS sediments may be a northerly ‘destroyed’ Neoproterozoic magmatic arc whose remnants exists within the Himalaya as the Neoproterozoic granitoids, and possibly be the iLH sedimentary belt, an ‘In-board’ Aravalli–Delhi Fold Belt (ADFB)–Central Indian Tectonic Zone (CITZ) in the south.

Oblique convergence and strain partitioning in the outer deformation front of NE Himalaya

Himalayan-Tibetan orogeny has considered as a natural black box in the context of geodynamic evolution and tectonic complexity. The eastward extrusion model of Tibetan crust contradicts with the oblique convergence model in the NE-Himalaya (Bhutan/Arunachal region), where the overall convergence rate accommodated in the Himalaya is about 20–25% less than that in the neighbouring central Himalaya and Eastern Himalayan syntaxis (EHS). We propose that instead of partitioning in the backarc, the NE-Himalaya has developed an active sliver along the Assam-Brahmaputra valley in the outer deformation front, in order to accommodate the deficiency in long-term plate convergence between Himalaya and southern Tibet. We argue that the strong eastward extrusion of Tibetan crust along NE-Himalaya is the main driving force for the unusual development of the Assam-Brahmaputra sliver. This new hypothesis can explain active convergence along EHS, low convergence and subdued topography in Bhutan and Arunachal Himalaya, kinematic and space-problem of Indo-Burmese wedge, and finally solves the contradiction between Tibetan extrusion and oblique convergence model of the HimalayanTibetan orogeny.

Elemental and Sr-Nd isotopic geochemistry of Mesoproterozoic sedimentary successions from NE Lesser Himalaya, northern India: Implications for Proterozoic climate and tectonics

The sedimentation history of northeastern Himalayan Proterozoic basins is poorly known. In the current study, we examine major, trace, rare earth elements (REEs) and Sr-Nd isotope geochemistry of pelites and quartzites from Mesoproterozoic metasedimenatary sequences of Bomdila and Rupa Groups, NE Himalaya in order to understand provenance, tectonic setting and paleoweathering conditions of deposition. The salient geochemical parameters, such as, high SiO2 and Al2O3 concentrations, relatively low MgO values, typical enrichment of immobile incompatible elements (Al2O3/TiO2 = 32.2, Th/Sc = 2.1), fractionated REE patterns (La/Ybn = 28) and a strong negative europium anomaly (Eu/Eu∗ = 0.3–0.7) indicate dominant felsic source for Bomdila sediments. Bomdila sediments show significantly radiogenic εNd0.95Ga values (−10.25 to −17.90, avg. −15.24) compared to Bundelkhand craton (avg. −26) and Singhbhum craton (avg. −30) and yield much younger TDM ages (2.3–2.7 Ga) compared to Archean Bundelkhand (3.2–3.5 Ga) and Singhbhum cratons (3.4–3.9 Ga). These results clearly rule out any significant detritus contribution from old cratonic sources. εNd and TDM data of Mesoprterozoic Bomdila sediments envelop the signature of Lower Proterozoic Inner Lesser Himalayan (ILH) terrane. Prominent U-Pb age peaks at 1702, 1651, ∼1400, 1248 and 1118 Ma in detrital zircons indicate major contribution from Late Paleoroterozoic to Late Mesoproterozic sources. However, initial Nd isotope ratios and TDM do not favour any juvenile inputs. We argue that ILH source terrain may have been extensively reworked during Late Paleoroterozoic to Late Mesoproterozic time and could have been part of a long lived orogenic belt.. Severe depletion of Ca, Na and Sr in Bomdila sediments indicate intense chemical weathering of the source region, and can be attributed to warm and humid climatic conditions, a conclusion which is consistent with the CO2-rich atmosphere during Mesoproterozoic period.

MORPHOMETRIC ANALYSIS OF THE GAI RIVER BASIN, NE HIMALAYA, INDIA.

24Jun 2017 MORPHOMETRIC ANALYSIS OF THE GAI RIVER BASIN, NE HIMALAYA, INDIA. Sorat Konwar. Department of Geology, Dimoria College, Khetri.

Transverse tectonic structural elements across Himalayan mountain front, eastern Arunachal Himalaya, India: Implication of superposed landform development on analysis of neotectonics

Structural and morphotectonic signatures in conjunction with the geomorphic indices are synthesised to trace the role of transverse tectonic features in shaping the landforms developed along the frontal part of the eastern Arunachal sub-Himalaya. Mountain front sinuosity (Smf) index values close to one are indicative of the active nature of the mountain front all along the eastern Arunachal Himalaya, which can be directly attributed to the regional uplift along the Himalayan Frontal Thrust (HFT). However, the mountain front is significantly sinusoidal around junctions between HFT/MBT (Main Boundary Thrust) and active transverse faults. The high values of stream length gradient (SL) and stream steepness (Ks) indices together with field evidence of fault scarps, offset of terraces, and deflection of streams are markers of neotectonic uplift along the thrusts and transverse faults. This reactivation of transverse faults has given rise to extensional basins leading to widening of the river courses, providing favourable sites for deposition of recent sediments. Tectonic interactions of these transverse faults with the Himalayan longitudinal thrusts (MBT/HFT) have segmented the mountain front marked with varying sinuosity. The net result is that a variety of tectonic landforms recognized along the mountain front can be tracked to the complex interactions among the transverse and longitudinal tectonic elements. Some distinctive examples are: in the eastern extremity of NE Himalaya across the Dibang River valley, the NW-SE trending mountain front is attenuated by the active Mishmi Thrust that has thrust the Mishmi crystalline complex directly over the alluvium of the Brahmaputra plains. The junction of the folded HFT and Mishmi Thrust shows a zone of brecciated and pulverized rocks along which transverse axial planar fracture cleavages exhibit neotectonic activities in a transverse fault zone coinciding with the Dibang River course. Similarly, the transverse faults cut the mountain front along the Sesseri, Siluk, Siku, Siang, Mingo, Sileng, Dikari, and Simen rivers. At some such junctions, landforms associated with the active right-lateral strike-slip faults are superposed over the earlier landforms formed by transverse normal faults. In addition to linear transverse features, we see evidence that the fold-thrust belt of the frontal part of the Arunachal Himalaya has also been affected by the neotectonically active NW-SE trending major fold known as the Siang antiform that again is aligned transverse to the mountain front. The folding of the HFT and MBT along this antiform has reshaped the landscape developed between its two western and eastern limbs running N-S and NW-SE, respectively. The transverse faults are parallel to the already reported deep-seated transverse seismogenic strike-slip fault. Therefore, a single take home message is that any true manifestation of the neotectonics and seismic hazard assessment in the Himalayan region must take into account the role of transverse tectonics.

Slope failure in stratified rocks: a case from NE Himalaya, India

Mountainous regions of India experience recurrent slope failures due to rapid urbanization. The main causes of slope failure are high precipitation aided by unplanned construction of cut slopes. Such slope failures are further aggravated because of the presence of low strength, highly jointed, stratified rocks rich in clay minerals. In general, effect of weathering is more pronounced in these rocks, which causes long-term time-dependent deterioration of the rocks as well as joint strength. In this regard, the present investigation deals with the causes, behavior, and mechanism of slope failure by examining a section in the North Eastern Himalayas. A detailed field investigation was carried out for examining the existing condition of slope, slope material, and joint parameters. Laboratory experiments like compressive and tensile strength tests along and across the lamination planes along with slake durability index tests were conducted to characterize the material and investigate the role of weathering in strength degradation. Later, numerical simulation was performed employing distinct element method to investigate the failure behavior, mechanism, and also the effect of water pressure in destabilizing the slope. The experimental result indicates directional strength variations parallel and perpendicular to bedding plane, which makes the rock incompetent to sustain external load. The presence of orthogonal joint sets accelerates the process of block detachment. Significant slaking was observed which further deteriorates and fragments the rock at deeper level. Numerical simulation shows that failure plane is dominantly planar (along the bedding parallel joints) and surficial.

Paleofloods records in Himalaya

We use paleoflood deposits to reconstruct a record of past floods for the Alaknanda-Mandakini Rivers (Garhwal Himalaya), the Indus River (Ladakh, NW Himalaya) and the Brahmaputra River (NE Himalaya). The deposits are characterized by sand-silt couplets, massive sand beds, and from debris flow sediment. The chronology of paleoflood deposits, established by Optically Stimulated Luminescence (OSL) and 14C AMS dating techniques, indicates the following: (i) The Alaknanda-Mandakini Rivers experienced large floods during the wet and warm Medieval Climate Anomaly (MCA); (ii) the Indus River experienced at least 14 large floods during the Holocene climatic optimum, when flood discharges were likely an order of magnitude higher than those of modern floods; and (iii) the Brahmaputra River experienced a megaflood between 8 and 6ka. Magnetic susceptibility of flood sediments indicates that 10 out of 14 floods on the Indus River originated in the catchments draining the Ladakh Batholith, indicating the potential role of glacial lake outbursts (GLOFs) and/or landslide lake outbursts (LLOFs) in compounding flood magnitudes. Pollen recovered from debris flow deposits located in the headwaters of the Mandakini River showed the presence of warmth-loving trees and marshy taxa, thereby corroborating the finding that floods occurred during relatively warm periods. Collectively, our new data indicate that floods in the Himalaya largely occur during warm and wet climatic phases. Further, the evidence supports the notion that the Indian Summer Monsoon front may have penetrated into the Ladakh area during the Holocene climatic optimum.

Impact of Neotectonism in the Discussion of Geomorphological Processes as a Feedback System: North Bengal Foothills, West Bengal

The ongoing research paper is concerned about the sensitive issue like neotectonism and its impact on the landscape development. It is a detail and micro level study of North Bengal Himalayan foothills where the effect of tectonism is precisely observed. The term, neotectonism was introduced by Obruchen (1948) to summarize the active tectonic processes including the last major tectonic configuration change and establishment of modern stress. The North Bengal Himalayan foothill are very much concerned about the neotectonism activities at last to present geological periods. It is the one of the active unstable area of NE India where faults/thrusts and presence of synformal axis are predominantly controlling the geomorphological landscape development. This frontal region of an active orogenic beltlikethe NE Himalaya is characterized by complex terrace morphology with fluvial aggradation, degradationandstrath terraces. The detail study is mainly about the lineaments, drainage sequences, thrusting zone and synformal depressed zone of the area. Near the Neora-Mal river valley, close to to the mountain front a thick supported boulder bed with huge angular boulders of gneisses are exposed near Neora valley of Samsing area. Concerning the fault zone area of Matiali scarp, it is very clearly observed the extended part of Garubathan thrust (MBT) under the Matiali formation near the upper part of Kurtiriver. But, in the middle part of the river, where the synformation axis is present, river terraces are magnificiently developed over two sides of R. Kurti near Matiali hat. Here, two terraces are well virtualized but the upper most flat terrain is designated as fan surface which is made of mainly by the sediments of Matialiformation. In this region, slope of the fan surface is southerly 2.1˚. In south of the Matiali scarp on the banks of R. Neora, Kurti, Murti raised terraces are distinctly observed as T1 and T2.There kinds of features have developed due to the active tectonic activities from last Pleistocene to recent Holocene. As an evidence , we can consider the recent seismic study with in meizoseismal zone of both the 1934 Bihar-Nepal and 1950 Assam earthquakes but last surface rupture with a recorded displacement of 14m of Chalsafault related to the historical earthquake in Nepal around 1100 AD (Kumar et.al. 2011). It is a positive feedback system where neotectonism and geomorphological landscape are well related and in a classical model of fault propagation; geomorphic evolution through the structure/process is present in respect of time and space.

Kinematics and strain rates of the Eastern Himalayan Syntaxis from new GPS campaigns in Northeast India

Newly acquired GPS data along transects across Himalaya in Eastern Himalayan Syntaxis (EHS) reveal a clockwise rotation of rigid micro-plate comprising part of Brahmaputra valley, NE Himalaya and Northern Myanmar that rotates about a pole located at 14.5°N, 100.8°E at an angular rate of 1.75±0.12°/Myr. The EHS is being torn-off from the main Indian Plate as a rigid block around which the kinematic clockwise rotation of Tibetan GPS sites toward the Sichuan-Yunnan region occurs in the Eurasia fixed frame. The residual velocity field of the newly acquired data estimated after removing the rotation that minimizes the GPS rates around EHS show a clear NE motion of the EHS sites, indentation of the rigid Indian plate into a less rigid area of the Eurasian plate. The most extensive EHS zones of compression and shortening are in the direction of indenter convergence, with average values ranging between ~50–100 nanostrain/year. Along the frontal segment of EHS, from NW to SE, the shortening rate is reduced from the local maximum value of 160 to ~80 nanostrain/year, thus indicating a possibly locked fault patch of Mishmi or Lohit thrusts, the southernmost part of segment activated during the large 1950 Assam earthquake, Mw 8.6.An elastic block-model was invoked to infer the average slip rates of sections around EHS and to estimate an average locking depth of ~15km. The slip rate perpendicular to the locked sector of EHS reaches 32.4mm/year and permits to roughly infer a recurrence time of ~200year for an earthquake as energetic as the 1950 Assam event.

Drainage migration and out of sequence thrusting in Bhalukpong, Western Arunachal Himalaya, India

In the foreland regions of the Western Arunachal Himalaya (WAH), geological studies along the Kameng river (between Tipi village and the Himalayan Frontal Thrust (HFT)) reveal four levels of unpaired terraces and a paired terrace. In WAH, wrench deformation of HFT zone resulted in a SE propagation of the Balipara anticline and it is suggested that the Mikir high basement controls its orientation. Ages of terrace surfaces from Siwaliks suggest that since the Late Pleistocene, Kameng River migrated at a rate varying between ∼7.5cm/yr in upper reaches and ∼13.5cm/yr towards northeast due to HFT related uplift. In the Brahmaputra plains, luminescence ages of abandoned paleochannel deposits suggest eastward shifting of the Kameng river at an average rate of ∼1m/yr. Field evidences between Bhalukpong and Tipi villages show Pliocene strath and Quaternary terrace surfaces, displaced by faults that do not correspond to the mapped faults in the foreland region. We interpret them as out-of-sequence thrusts (OOSTs). This is the first such report of OOST in the NE Himalaya. Presence of active OOST is inferred by similar age (∼1ka) and differing incision rates of the surface of same terrace (T2b) in adjacent locations. This suggests that OOSTs in the western Arunachal Siwalik are <1ka. Average slip rate and horizontal shortening rate on OOST during the Holocene, are calculated as ∼12mm/yr and 7mm/yr respectively. Thus any estimation of Holocene shortening in the Siwalik therefore, needs to incorporate slip along the OOSTs given that it accommodates a significant amount of N-S compression of the Himalayan fold-and-thrust belt. The reason for OOST in the WAH Siwalik foreland is discussed in terms of the critical wedge dynamics arising from erosion via tectonics-climate interaction. We estimate a minimum slip rate of Siwalik as ∼27mm/yr during the Holocene and suggest acceleration in shortening rates east of Bhutan.

Atmospheric particulate matter (PM2.5), EC, OC, WSOC and PAHs from NE–Himalaya: abundances and chemical characteristics

Atmospheric concentrations of elemental, organic and water–soluble organic carbon (EC, OC and WSOC) and polycyclic aromatic hydrocarbons (PAHs) have been studied in PM2.5 (particulate matter of aerodynamic diameter ≤2.5 μm) from a site (Barapani: 25.7 °N; 91.9 °E; 1 064 m amsl) in the foot–hills of NE–Himalaya (NE–H). Under favorable wind–regimes, during the wintertime (January–March), study region is influenced by the long–range transport of aerosols from the Indo–Gangetic Plain (IGP). For rest of the year, ambient atmosphere over the NE–H is relatively clean due to frequent precipitation events associated with the SW– and NE–monsoon. The concentration of PM2.5 over NE–H, during the wintertime, varied from 39–348 μg m–3, with average contribution of OC and EC as 36±8% (AVG±SD) and 6±3%, respectively. For the OC/EC ratio as high as 10–15 (relatively high compared to fossil–fuel source) associated with WSOC/OC ratio exceeding 0.5 in NE–H, it can be inferred that dominant source of carbonaceous aerosols is attributable to biomass burning emissions and/or contributions from secondary organic aerosols (SOA). The OC/PM2.5 ratio from NE–H is somewhat higher compared to upwind regions in the IGP (Range: 0.16–0.24). The abundance of ΣPAHs show large variability, ranging from 4–46 ng m–3, and the ratio of sum of 4– to 6–ring PAHs (Σ(4– to 6–) PAHs) to EC is 2.4 mg g–1; similar to that in the upwind IGP and is about a factor of two higher than that from the fossil–fuel combustion sources. The cross-plot of PAH isomers [FLA/(FLA+PYR) vs. ANTH/(ANTH+PHEN), BaA/(BaA+CHRY+TRIPH), BaP/(BaP+B[b,j,k]FLA) and IcdP/(IcdP+BghiP)] reaffirms the dominant impact of biomass burning emissions. These results have implications to large temporal variability in aerosol radiative forcing and environmental change over the NE–Himalaya.

Diversity of Middle Eocene Coralline Red Algae from the Prang Limestone (Shella Formation) of Jaintia Hills, Meghalaya, NE Himalaya, India with special emphasis on palaeoenvironment

Palaeocene-Eocene carbonates of shallow marine sequence belonging to Shella Formation of Jaintia Group are well developed in the south of the Jaintia Hills, Meghalaya and represent an excellent outcrop of shelf sediments in North Eastern Himalaya, India. These outcrops are exposed along the southern fringe of Shillong Plateau. The Prang Limestone is the uppermost lithostratigraphic unit of the Shella Formation within the Jaintia Group. It is overlain by sand-shale alternation of the Kopili Formation and underlain by the Narpuh Sandstone. A rich assemblage of larger foraminifera including Nummulites, Discocyclina etc. has been recorded earlier from the Prang Limestone and based on the foraminiferal assemblage, a Middle Eocene to Early Late Eocene age has been assigned to the Prang Limestone. Thin section analysis of the Prang Limestone revealed the abundance of well preserved coralline red algae along with other well preserved and significant biogenic elements. Morpho-taxonomical study reveals that the algal flora is represented by seven species belonging to the families Hapalidiaceae (Subfamily: Melobesioideae), Corallinaceae (Subfamily: Mastophoroideae) and Sporolithaceae. The dominance of melobesioid and mastophoroid forms is the characteristic feature of this algal assemblage. Coralline algae occur mostly in encrusting growth form with orbitoid foraminifera and occasionally the coralline algae form rhodoliths. On this basis of algal forms it can be inferred that they thrived in a shallow, warm, shelf environment of normal salinity.