Article ID 0107 December 2017
The eclogites of the Tso Morari Complex, Ladakh, NW Himalayas preserve both garnets with spectacular atoll textures, as well as whole porphyroblastic garnets. Whole garnets are euhedral, idiomorphic and enclose inclusions of amphibole, phengite and zoisite within the cores, and omphacite and quartz/coesite towards the rims. Detailed electron microprobe analyses and back-scattered electron images show well-preserved prograde zoning in the whole garnets with an increase in Mg and decrease in Ca and Mn contents from the core to the rim. The atoll garnets commonly consist of euhedral ring over island/peninsular core containing inclusions of phengite, omphacite and rarely amphibole between the core and ring. Compositional profiles across the studied atoll grains show elemental variations with higher concentrations of Ca and Mn with low Mg at the peninsula/island cores; contrary to this low Ca, Mn and high Mg is observed at the outer rings. Temperature estimates yield higher values at the Mg-rich atoll garnet outer rings compared to the atoll cores. Atoll garnet formation was favoured by infiltration of fluid formed due to breakdown of hydrous phases, and/or the release of structurally bounded OH from nominally anhydrous minerals at the onset of exhumation. Infiltration of fluids along pre-existing fracture pathways and along mineral inclusion boundaries triggered breakdown of the original garnet cores and released elements which were subsequently incorporated into the newly-grown garnet rings. This breakdown of garnet cores and inward re-growth at the outer ring produced the atoll structure. Calibrated geo-thermobarometers and mineral equilibria reflect that the Tso Morari eclogites attain peak pressures prior to peak temperatures representing a clockwise path of evolution.
Article ID 0108 December 2017
Precipitation samples were collected across the Himalayas from Kashmir (western Himalaya) to Assam (eastern Himalaya) to understand the variation of the stable isotopic content (δ18O and δD) in precipitation associated with two dominant weather systems of the region: western disturbances (WDs) and Indian summer monsoon (ISM). Large spatial and temporal variations in isotopic values were noted with δ18O and δD values ranging from −30.3 to +9.3 ‰ and −228 to +59‰, respectively. The d-excess values also exhibit a large range of variation from −30 to +40‰. In general, heavier isotopic values are observed in most of the samples in Jammu, whereas lighter values are observed in majority of the samples in Uttarakhand. Precipitation at Jammu seems to have undergone intense evaporation while that from Uttarakhand suggest normal Rayleigh fractionation/distillation of the air mass as it moves from the source region to the precipitation site and/or orographic lifting. The d-excess of rainfall in Kashmir has a distinctly higher median value of +18‰ compared to other precipitation sites with a median of 9−12‰. Using distinct isotopic signatures, the regions receiving precipitation from two different weather systems have been identified.
Article ID 0109 December 2017
Groundwater potential analysis prepares better comprehension of hydrological settings of different regions. This study shows the potency of two GIS-based data driven bivariate techniques namely statistical index (SI) and Dempster–Shafer theory (DST) to analyze groundwater potential in Broujerd region of Iran. The research was done using 11 groundwater conditioning factors and 496 spring positions. Based on the ground water potential maps (GPMs) of SI and DST methods, 24.22% and 23.74% of the study area is covered by poor zone of groundwater potential, and 43.93% and 36.3% of Broujerd region is covered by good and very good potential zones, respectively. The validation of outcomes displayed that area under the curve (AUC) of SI and DST techniques are 81.23% and 79.41%, respectively, which shows SI method has slightly a better performance than the DST technique. Therefore, SI and DST methods are advantageous to analyze groundwater capacity and scrutinize the complicated relation between groundwater occurrence and groundwater conditioning factors, which permits investigation of both systemic and stochastic uncertainty. Finally, it can be realized that these techniques are very beneficial for groundwater potential analyzing and can be practical for water-resource management experts.
Article ID 0110 December 2017
A concrete study combining optical microscopy, Raman spectroscopy and X-ray diffractometry, was carried out on subsurface samples of basement granite and melt breccia from Mohar (Dhala) impact structure, Shivpuri district, Madhya Pradesh, India. Optical microscopy reveals aberrations in the optical properties of quartz and feldspar in the form of planar deformation feature-like structures, lowered birefringence and mosaics in quartz, toasting, planar fractures and ladder texture in alkali feldspar and near-isotropism in bytownite. It also brings to light incidence of parisite, a radioactive rare mineral in shocked granite. Raman spectral pattern, peak positions, peak widths and multiplicity of peak groups of all minerals, suggest subtle structural/crystallographic deviations. XRD data further reveals minute deviations of unit cell parameters of quartz, alkali feldspar and plagioclase, with respect to standard α-quartz, high- and low albite and microcline. Reduced cell volumes in these minerals indicate compression due to pressure. The c0/a0 values indicate an inter-tetrahedral angle roughly between 120o and 144o, further pointing to a possible pressure maxima of around 12 GPa. The observed unit cell aberration of minerals may indicate an intermediate stage between crystalline and amorphous stages, thereby, signifying possible overprinting of decompression signatures over shock compression effects, from a shock recovery process.
Article ID 0111 December 2017
In boreal summer (June–September), most of the Indian land and its surroundings experience rainrates exceeding 6 mm day−1 with considerable spatial variability. Over southern Bay of Bengal (BoB) along the east coast of the Indian peninsula (henceforth referred to as the Bay of Bengal cold pool or BoB-CP), the rain intensity is significantly lower (<2 mm day−1) than its surroundings. This low rainfall occurs despite the fact that the sea surface temperature in this region is well above the threshold for convection and the mean vorticity of the boundary layer is cyclonic with a magnitude comparable to that over the central Indian monsoon trough where the rainrate is about 10 mm day−1. It is also noteworthy that the seasonal cycle of convection over the BoB-CP shows a primary peak in November and a secondary peak in May. This is in contrast to the peak in June–July over most of the oceanic locations surrounding the BoB-CP. In this study, we investigate the role of the Western Ghat (WG) mountains in an Atmospheric General Circulation Model (AGCM) to understand this paradox. Decade-long simulations of the AGCM were carried out with varying (from 0 to 2 times the present) heights of the WG. We find that the lee waves generated by the strong westerlies in the lower troposphere in the presence of the WG mountains cause descent over the BoB-CP. Thus, an increase in the height of the WG strengthens the lee waves and reduces rainfall over the BoB-CP. More interestingly in the absence of WG mountains, the BoB-CP shows a rainfall maxima in the boreal summer similar to that over its surrounding oceans. The WG also impacts the climate over the middle and high latitude regions by modifying the upper tropospheric circulation. The results of this study underline the importance of narrow mountains like the WG in the tropics in determining the global climate and possibly calls for a better representation of such mountains in climate models.
Article ID 0112 December 2017
Several deformation phases in tectonically active Himalayas have rendered the rock masses very complex in terms of structure, lithology and degree of metamorphism. Again, anthropogenic activities such as roads, tunnels and other civil engineering constructions have led to a state of disequilibrium which in many cases, results in failure of rock masses. National Highway-05 around Jhakri area in India is a major connecting route to the China border in the hilly terrains of the state Himachal Pradesh. It cuts through the Himalayan rocks and has a hazardous history of landslides destroying human lives and interrupting communication very frequently. As a contribution towards the mitigation process, a study has been carried out along the highway to analyse kinematic stability and qualitative estimation of rock mass condition through rock mass classification systems. The kinematic analysis shows that the rock slopes are prone to planar and wedge failure. Rock mass rating for most of the locations lies between 7 and 34, representing a poor rock mass quality (Class IV), whereas slope mass rating is more disperse and ranges from 11 to 52 for most of the slopes (Class III, IV and V).
Article ID 0113 December 2017
Owing to the lack of consistent spatial time series data on actual evapotranspiration (ET), very few studies have been conducted on the long-term trend and variability in ET at a national scale over the Indian subcontinent. The present study uses biome specific ET data derived from NOAA satellite’s advanced very high resolution radiometer to investigate the trends and variability in ET over India from 1983 to 2006. Trend analysis using the non-parametric Mann–Kendall test showed that the domain average ET decreased during the period at a rate of 0.22 mm year−1. A strong decreasing trend (m=−1.75 mm year−1, F=17.41, P 0.01) was observed in forest regions. Seasonal analyses indicated a decreasing trend during southwest summer monsoon (m=−0.320 mm season−1year−1) and post-monsoon period (m=−0.188 mm season−1year−1). In contrast, an increasing trend was observed during northeast winter monsoon (m=0.156 mm season−1year−1) and pre-monsoon (m=0.068mm season−1year−1) periods. Despite an overall net decline in the country, a considerable increase ( 4 mm year−1) was observed over arid and semi-arid regions. Grid level correlation with various climatic parameters exhibited a strong positive correlation (r> 0.5) of ET with soil moisture and precipitation over semi-arid and arid regions, whereas a negative correlation (r−0.5) occurred with temperature and insolation in dry regions of western India. The results of this analysis are useful for understanding regional ET dynamics and its relationship with various climatic parameters over India. Future studies on the effects of ET changes on the hydrological cycle, carbon cycle, and energy partitioning are needed to account for the feedbacks to the climate.
Article ID 0114 December 2017
Orography profoundly influences seasonal rainfall amount in several places in south Asia by affecting rain intensity and duration. One of the fundamental questions concerning orographic rainfall is nature of the associated precipitating clouds in the absence of synoptic forcing. It is believed that these clouds are not very deep, however, there is not much information in the literature on their vertical structure. The present study explores the vertical structure of precipitating clouds associated with orographic features in south Asia using data collected with the precipitation radar on board the Tropical Rainfall Measuring Mission satellite. Two types of precipitating clouds have been defined based on cloud echo top height, namely, shallow echo-top cloud and medium echo-top cloud. In both, radar reflectivity factor is at least 30 dBZ at 1.5 km altitude, and tops of shallow and medium echo-top clouds lie below 4.5 km and between 4.5 and 8 km, respectively. The Western Ghats contains the highest fraction of the shallow echo-top clouds followed by the adjacent eastern Arabian Sea, while the Khasi Hills in Meghalaya and Cardamom Mountains in Cambodia contain the least fraction of them. Average vertical profiles of shallow echo-top clouds are similar in different mountainous areas while regional differences are observed in the medium echo-top clouds. Below 3 km, precipitation liquid water content in medium echo-top clouds is the highest over the Western Ghats and the eastern Arabian Sea. The average precipitation liquid water content increases by 0.16 gm m−3 for shallow echo-top clouds between 3 and 1.5 km altitude, while the corresponding increase for medium echo-top clouds is in 0.05–0.08 gm m−3 range.
Article ID 0115 December 2017
The present study provides improved chronology for the desert margin fluvial sediments of semi-arid region located in the Mahi river basin, western India. The sequence has preserved a near-continuous record of climate change since the Last Interglacial. An earlier attempt of dating based on feldspar IRSL chronology shows a combined effect of anomalous fading and unbleached components resulting in age inversions. The present work tries to explore the possibility of using blue light stimulated luminescence (BLSL) of quartz, infra-red stimulated luminescence (IRSL) of feldspar and the newly developed methodologies, like natural correction factor based single aliquot regeneration (NCF-SAR) protocol and decision making schemes based on distribution of doses and beta heterogeneity concept for luminescence dating of sediments. Observations suggest that quartz suffered from significant sensitivity changes during natural signal measurement and partial bleaching. A combination of NCF-SAR protocol and sample specific equivalent dose computation helped in arriving at better age estimate for present samples. The study also compares the criteria for the selection of different age models that are used at present. The age of the alluvial sequence is now bracketed between 10 ka (upper aeolian unit) and 75 ka (lowermost fluvial unit).
Article ID 0116 December 2017
Rapid debris flows, a mixture of unconsolidated sediments and water travelling at speeds >10 m/s are the most destructive water related mass movements that affect hill and mountain regions. The predisposing factors setting the stage for the event are the availability of materials, type of materials, stream power, slope gradient, aspect and curvature, lithology, land use and land cover, lineament density, and drainage. Rainfall is the most common triggering factor that causes debris flow in the Palar subwatershed and seismicity is not considered as it is a stable continental region and moderate seismic zone. Also, there are no records of major seismic activities in the past. In this study, one of the less explored heuristic methods known as the analytical network process (ANP) is used to map the spatial propensity of debris flow. This method is based on top-down decision model and is a multi-criteria, decision-making tool that translates subjective assessment of relative importance to weights or scores and is implemented in the Palar subwatershed which is part of the Western Ghats in southern India. The results suggest that the factors influencing debris flow susceptibility in this region are the availability of material on the slope, peak flow, gradient of the slope, land use and land cover, and proximity to streams. Among all, peak discharge is identified as the chief factor causing debris flow. The use of micro-scale watersheds demonstrated in this study to develop the susceptibility map can be very effective for local level planning and land management.
Article ID 0117 December 2017
Timing and implications for the late Mesozoic geodynamic settings of eastern North China Craton: Evidences from K–Ar dating age and sedimentary–structural characteristics records of Lingshan Island, Shandong Province
The Lingshan Island in Shandong Province in the eastern North China Craton, well known for the Late Mesozoic multi-scale slide-slump structures is related to paleo-earthquake. Terrigenous clastic rocks, volcanic clastic rocks and volcanic lavas are extensively exposed in the Lingshan Island and its adjacent regions of the Shandong Province, which led to fierce debates on their ages, sedimentary characteristics and tectono-sedimentary evolution. In this contribution, we present the characteristics of the Late Mesozoic stratigraphy in the Lingshan Island. Whole-rock K–Ar dating of dyke at Beilaishi and rhyolites at Laohuzui of the Lingshan Island yielded ages of 159 Ma and 106–92 Ma which coincides with the Laiyang Period rifting and the Qingshan Period rifting in the Jiaolai Basin, respectively. On the basis of the analysis to the Late Mesozoic sedimentary environment of ‘flysch’ and ‘molasse’-like formations as well as tectonic stress fields reconstruction, four episodes of the tectono-sedimentary evolution were established in the Lingshan Island and its adjacent regions in the eastern North China Craton. They consist of two episodes of extensional events for the syn-rift, and two episodes of compression events for the inversion of the post-rift. The entire episodes can be summarized as follows: (1) the first syn-rift NW–SE extension in Laiyang Period can be identified by the ‘flysch’ formation (Unit 1) and by emplacement of the NE-trending dyke in the Laiyang Group. This syn-rift episode can be related to the NW–SE post-orogenic extension resulted from the gravity collapse of the thickened lithosphere along the Sulu Orogen. (2) The first post-rift NW–SE inversion, which was caused by the NW-directed subduction of Izanaqi Plate, can be well documented by the ‘X’ type conjugate joints as well as slide slump folds in Unit 1. (3) The second syn-rift NW–SE extension in Qingshan Period is characterized by rhyolite rocks (Unit 2). This syn-rift episode can be considered to be associated with lithospheric delamination of the thickened lithosphere in the eastern North China Craton. And finally, (4) the second post-rift NW–SE inversion which resulted from the subduction of the Pacific Plate under the eastern North China Craton in the NW direction at the end of the Qingshan Period is recorded by ‘molasse’-like formation (Unit 3).
Article ID 0118 December 2017
Oxygen (δ18O) and hydrogen (δ2H and 3H) isotopes of water, along with their hydrochemistry, were used to identify the source of a newly emerged seepage water in the downstream of Lake Nainital, located in the Lesser Himalayan region of Uttarakhand, India. A total of 57 samples of water from 19 different sites, in and around the seepage site, were collected. Samples were analysed for chemical tracers like Ca++, Mg++, Na+, K+, SO4−− and Cl− using an Ion Chromatograph (Dionex IC-5000). A Dual Inlet Isotope Ratio Mass Spectrometer (DIIRMS) and an Ultra-Low Level Liquid Scintillation Counter (ULLSC), were used in measurements of stable isotopes (δ2H and δ18O) and a radioisotope (3H), respectively. Results obtained in this study repudiate the possibility of any likely connection between seepage water and the lake water, and indicate that the source of seepage water is mainly due to locally recharged groundwater. The study suggests that environmental isotopes (δ2H, δ18O and 3H) can effectively be used as ‘tracers’ in the detection of the source of seepage water in conjunction with other hydrochemical tracers, and can help in water resource management and planning.
Article ID 0119 December 2017
Evapotranspiration (ET) plays an important role in exchange of water budget and carbon cycles over the Inner Mongolia autonomous region of China (IMARC). However, the spatial and decadal variations in terrestrial ET and drought over the IMARC in the past was calculated by only using sparse meteorological point-based data which remain quite uncertain. In this study, by combining satellite and meteorology datasets, a satellite-based semi-empirical Penman ET (SEMI-PM) algorithm is used to estimate regional ET and evaporative wet index (EWI) calculated by the ratio of ET and potential ET (PET) over the IMARC. Validation result shows that the square of the correlation coefficients (R2) for the four sites varies from 0.45 to 0.84 and the root-mean-square error (RMSE) is 0.78 mm. We found that the ET has decreased on an average of 4.8 mm per decade (p=0.10) over the entire IMARC during 1982–2009 and the EWI has decreased on an average of 1.1% per decade (p=0.08) during the study period. Importantly, the patterns of monthly EWI anomalies have a good spatial and temporal correlation with the Palmer Drought Severity Index (PDSI) anomalies from 1982 to 2009, indicating EWI can be used to monitor regional surface drought with high spatial resolution. In high-latitude ecosystems of northeast region of the IMARC, both air temperature (Ta) and incident solar radiation (Rs) are the most important parameters in determining ET. However, in semiarid and arid areas of the central and southwest regions of the IMARC, both relative humidity (RH) and normalized difference vegetation index (NDVI) are the most important factors controlling annual variation of ET.
Article ID 0120 December 2017
Meteorological drought during the southwest monsoon season and for the northeast monsoon season over five meteorological subdivisions of India for the period 1901–2015 has been examined using district and all India standardized precipitation index (SPI). Whenever all India southwest monsoon rainfall was less than −10% or below normal, for those years all India SPI was found as −1 or less. Composite analysis of SPI for the below normal years, viz., less than −15% and −20% of normal rainfall years indicate that during those years more than 30% of country’s area was under drought condition, whenever all India southwest monsoon rainfall was –15% or less than normal. Trend analysis of monthly SPI for the monsoon months identified the districts experiencing significant increase in drought occurrences. Significant positive correlation has been found with the meteorological drought over most of the districts of central, northern and peninsular India, while negative correlation was seen over the districts of eastern India with NINO 3.4 SST. For the first time, meteorological drought analysis over districts and its association with equatorial pacific SST and probability analysis has been done for the northeast monsoon over the affected regions of south peninsular India. Temporal correlation of all India southwest monsoon SPI and south peninsular India northeast monsoon SPI has been done with the global SST to identify the teleconnection of drought in India with global parameters.
Article ID 0121 December 2017
The Bundelkhand massif, located in the northern part of the Indian shield, is a poly-deformed and poly-metamorphic terrain. This paper reports a new shear system developed throughout the massif in the form of N–S trending quartz veins that are sometimes quartzo-feldspathic and rarely granitic in composition. The veins are vertical and commonly occur in conjugate sets. This tectono-magmatic event appears to represent the youngest shear system of the massif as it cross-cuts all the earlier shear systems (E–W, NE–SE and NW–SE). Emplacement of this N–S vein system may have taken place due to extensional processes that developed some cracks along which siliceous magma was vertically emplaced. The complete absence of signature of the N–S event from the surrounding sedimentary cover of Vindhyan Supergroup, Bijawar and Gwalior Groups suggests that this shear system is pre-tectonic to the nearly E–W trending passive basins developed at the margins of the Bundelkhand craton. Further, several workers have considered the Bundelkhand massif as a part of the Aravalli craton. However, due to the absence of N–S, as well as the other (i.e., E–W, NW–SE and NW–SE), tectonic fabrics of the Bundelkhand massif in other cratons of the Peninsular India, and vice versa, makes the Bundelkhand block a separate and unique craton of its own and is not part of the Aravalli craton.
Article ID 0122 December 2017
A review has been made to understand the hydrogeochemical behaviour of groundwater through statistical analysis of long term water quality data (year 2005–2013). Water Quality Index (WQI), descriptive statistics, Hurst exponent, fractal dimension and predictability index were estimated for each water parameter. WQI results showed that majority of samples fall in moderate category during 2005–2013, but monitoring site four falls under severe category (water unfit for domestic use). Brownian time series behaviour (a true random walk nature) exists between calcium (Ca2+) and electric conductivity (EC); magnesium (Mg2+) with EC; sodium (Na+) with EC; sulphate (SO2−4) with EC; total dissolved solids (TDS) with chloride (Cl−) during pre- (2005–2013) and post- (2006–2013) monsoon season. These parameters have a closer value of Hurst exponent (H) with Brownian time series behaviour condition (H=0.5). The result of times series analysis of water quality data shows a persistent behaviour (a positive autocorrelation) that has played a role between Cl− and Mg2+, Cl− and Ca2+, TDS and Na+, TDS and SO2−4, TDS and Ca2+ in pre- and post-monsoon time series because of the higher value of H (>1). Whereas an anti-persistent behaviour (or negative autocorrelation) was found between Cl− and EC, TDS and EC during pre- and post-monsoon due to low value of H. The work outline shows that the groundwater of few areas needs treatment before direct consumption, and it also needs to be protected from contamination.
Volume 129, 2020
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