Himachal Himalaya Research Articles

Environmental radioactivity: a case study in Himachal Pradesh, India

A radon survey has been carried out in the soil-gas and indoor air of some villages situated in the vicinity of areas known for uranium mineralisation in Himachal Pradesh (H.P.). Both active and passive techniques were used for radon monitoring inside the dwellings. The highest value, 75 400±2620 Bq m -3, of radon in soil-gas was found in the village of Samurkhurd. The mean values of indoor radon concentration for the village of Ramera, Asthota, and Galot were found to be 249±14, 200±16 and 161±13 Bq m -3, respectively. The average annual exposure doses due to radon and its daughter products to the inhabitants of these villages amount to 4.3±0.2, 3.4±0.3 and 2.8±0.2 mSv, respectively. Indoor radon levels are within the safe limits in most dwellings but call for mitigation of the radon health hazard in some others. A radon and helium survey of thermal springs in the Parbati and Kullu valleys of Himachal Himalaya was also carried out. The maximum values of radon (716.3 Bq l -1) and helium (90 ppm) activities were recorded in a thermal spring at Kasol in Parbati valley. In general, high radon and helium values are correlated with high uranium concentrations in the soil of the area in the environs of the thermal springs.

Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.

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

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]

Evidence for the thrust emplacement of the ‘Lesser Himalaya’ Chur granite, Himachal Pradesh

Numerous peraluminous and porphyritic granitic bodies and augen gneisses of granitic compositions occur in the nappe sequences of the Lower Himalaya. They are Proterozoic-to-lower Paleozoic in age and have been grouped into the ‘Lesser Himalaya granite belt’. The mode of emplacement and tectonic significance of these granites are as yet uncertain but they are generally considered to be sheet-like intrusions into the surrounding rocks. The small and isolated granite body (the Chur granite) that crops out around the Chur peak in the Himachal Himalaya is one of the more famous of these granites. Several lines of evidence have been adduced to show that the Chur granite has a thrust (the Chur thrust) contact with the underlying metasedimentary sequence (locally called the Jutogh Group). The Chur granite with restricted occurrence at the highest topographic and structural levels represents an erosional remnant of a much larger sub-horizontal thrust sheet. The contact relations between the country rocks and many of the other granite and granitic augen gneisses in the Lesser Himalaya belt are apparently similar to that of the Chur granite suggesting that at least some of them may also represent thrust sheets.

Morphology and facies of the alluvial-fan sedimentation in the Kangra Valley, Himachal Himalaya

A number of alluvial fans, having an average width (E-W) of 10–15 km and length (N-S) of 8–15 km, have been mapped using the LANDSAT TM imageries on 1:250,000 scale in the Kangra Valley of Himachal Himalaya. This important geomorphic zone of alluvial fans is confined between the foot of the Dhauladhar Range and the Siwalik ridges. These fans are gently sloping from north to south and are slightly dissected having distinct horizons of glacial, glacio-fluvial, fluvial, lacustrine and loessic sediments derived from the Dhauladhar granitic complex, Dharamsala and Siwalik Formations during the glacial and interglacial climatic stages of the Quaternary period. The vertical lithological profiles of these fans show a dominance of gravelly (nearly 60%) facies along with other lithofacies associations representing a braided-river depositional environment. In general, the thickness of fan sediments ranges between 90 and 120 m. The vertical facies are subdivided into three main facies, i.e. lower-, middle- and upper-fan facies, showing distinct sediment characteristics. The presence of glacial moraines and clay-rich debris-flow deposits is significant in the upper-fan facies. The middle-fan facies is gravel-dominated along with some interbedded sandy channel-fill deposits, whereas the lower-fan facies is composed of sand, silt and mud. The genesis of these three fan facies is closely related with the uplift of the source area and climatic changes during the Pleistocene period.

Space and time variation in the seismicity patterns preceding two earthquakes in the Himachal Pradesh, India

Seismicity patterns associated with two earthquakes on November 5, 1968 ( M L = 5.0) and June 14, 1978 ( M L = 5.4) in the Himachal Himalayas were studied by monitoring earthquakes through a close network of Seismic stations in the region. Hypocentre locations of 1100 earthquakes during the period 1965 to 1982 in the magnitude range 2 $ ̌ / M ⩽ 6 on the Richter Scale in the grid 32°–33° N, 76°–77° E were determined and an epicentral map for each year is presented superimposing LANDSAT imagery. The focal mechanisms of these two earthquakes were also studied from P-wave motion data. It has been observed that the focal mechanisms of both the earthquakes were similar and do not follow the regional trend in conformity with the concept of plate tectonics. The focal mechanism is, however, attributed to lineaments close to Dharamsala identified from LANDSAT imagery. It is interesting to observe that the two earthquakes show marked variations in aftershock activity. The migration pattern of the earthquakes after the occurrence of the main shocks show similar trends but differ in velocity of migration. Space-time variations in seismicity patterns associated with these two earthquakes show an increase of seismic activity followed by a period of relative quiescence in the neighbourhood of epicentres of earthquakes and expected rupture zones.

Observed amplitude changes and seismic activity prior to two recent earthquakes in the Himachal Himalayas, India

The amplitude ratio of P to S waves measured on a vertical component seismograph from foreshocks and aftershocks to two recent Himachal Himalayan earthquakes in India exhibits a characteristic change at the time of the main events. This change was accompanied by simultaneous first motion changes at nearby stations. The variation is a function of the orientations of the earthquake source. Migration of foreshocks activity prior to the occurrence of these earthquakes suggests the possibility of the presence of a number of micro tear faults in the region.

Fission-track ages from the pandoh-baggi area, himachal himalaya, and their tectonic interpretations

Apatite fission-track ages with different cover heights from the Pandoh—Baggi Tunnel, a part of the Beas—Satluj Link Project in Himachal Pradesh (India), have been measured to range from 7 to 27 m.y. The relation between the age and cover height is found to be linear. The in situ apatite track analyses have been used to compute the average rates of uplift and cooling for Mandi granite as 0.06 mm/year and ~5°C/m.y., respectively.

Palaeozoic granites and their younger components - A study of Mandi and Rakcham granites from the Himachal Himalaya

DOI = 10.3126/hjs.v5i7.1278 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.82-83

Geochemical characters of muscovite from the Pan African Mandi Granite, and its emplacement and evolution

DOI = 10.3126/hjs.v5i7.1291 Himalayan Journal of Sciences Vol.5(7) (Special Issue) 2008 p.98