001180   Borgohain P;Gohain K;Gogoi D K;Phukan M K (Dep of Appl Geol, Dibrugarh Univ, Assam) : Reservoir properties, provenance and depositional model of lower eocene clastic sequence (Lakadong+Therria) of a part of upper Assam Shelf. Indian J Petrol Geol 2004, 13(2), 31-51.

Clastic sequence of Lower Eocene age (locally known as Lakadong + Therria) overlying the Basement and the underlying the Sylhet Formation has been encountered in subsurface in a number of deep wells in the Oil India Limited's operational area of upper Assam Shelf. Discovery of this clastic petroleum reservoir in the late eighties has set an important landmark in the history of oil exploration. The Lakadong + Therria Member can be subdivided into three lithofacies of respective lower, middle and upper counterparts. The lower unit is characterized by thin interbedded sandstone, shale, siltstone and carbonaceous shale/coal. The middle unit is characterized by thick sandstone and shale with occasional abundance of calcareous sandstone. The upper unit is characterized by relatively thick shale and (sometimes siltstone) sandstone alternation. Calcareous sandstone predominantly occurs in this unit. Precipitation of secondary minerals like chert, mica and replacement of framework grains and precipitation of carbonate cements are the representatives of chemical causes of porosity reduction in certain producing horizons of this clastic reservoir. On the other hand, fracturing of quartz grains, dissolution of feldspar grains and secondary development of microcrystalline quartz grains which prevents the quartz overgrowth over large grain surfaces are some of the important diagenetic changes that contribute towards the development of secondary porosity in the sandstone of present study. Petrographic analysis, heavy mineral analysis, SEM study and geochemical study infer that these sediments were derived from varied sources in which igneous and faietamorphic sources have contributed major portion and were deposited in a near shore marshy/lagoonal to prograding barrier bar tidal system.

12 illus, 2 tables, 28 ref,

001179   Bhatt D K;Prasad S;Jain R l;Mathur A K (NO, , 57, Clay Square, Lucknow-226 001, Email: dkbhatt3@yahoo.co.in) : Some critical field observations on the genesis and stratigraphical status of Pokaran boulder bed, Western Rajasthan. J Geol Soc India 2005, 65(3), 301-8.

Based on the present detailed field observations on the physiographic setting and the lithological nature of the Pokran Boulder Bed (PBB), the authors conclude that it is a consolidated sedimentary bed, apparently in the nature of a glacial drift and not a tillite (like Talchir Formation of Gondwana Supergroup). The denuded upper surface of bouldery hummocks of the PBB on the ground invariably shows presence of loose boulders. The consolidated horizons lie buried within the hummocks, wherever thicker horizons of PBB are still preserved. The weathered top of the PBB, forming rolling, hummocky topography is reminiscent of continental glaciated areas. It is likely that the PBB represents remnant of the well-known global Precambrian (Vendian) Ice Age. It rests directly over the rhyolitic (Malani Rhyolite) basement. The field observations also lead to the conclusion that the thick succession of sandstones of the Jodhpur Group (sometimes referred as 'Jodhpur sandstone') of Marwar Supergroup, (MSG) only occasionally overlie the PBB and always with a marked unconformity, such as at Gaphur Khan ki Dhani and elsewhere. Clearly the PBB does not form part of the stratigraphy of Marwar Supergroup.

10 illus, 14 ref

001178   Bayhan E;Hasdigen S (Hacettepe Univ Dep of Geol Engng, , 06532 Beytepe, Ankara, Turkey, Email: ebayhan@hacetteppe.edu.tr) : Sedimentary petrology of tertiary deposits in a recycled orogenic area, Kale-Denizli, Western Turkey. J Geol Soc India 2005, 65(4), 482-6.

Sedimentary petrology of Tertiary deposits of Kale-Denizli area of southwestern Turkey is presented. Coupled with heavy mineral studies, the results obtained permit one to conclude that these sediments are products of a recycled orogen.

^ssc4 illus, 2 tables, 27 ref

001177   Babu H V R;Lakshmi M P (Natn Geophys Res Inst, , Hyderabad-500 007, Email: rambabungri@rediffmail.com) : A note on geophysical mapping of the granulite terranes surrounding the godavari basin. J Geol Soc India 2005, 65(2), 211-6.

Regional gravity and aeromagnetic data over the Godavari basin and the adjoining region show distinct signatures of granulite terranes of Karimnagar and Bhopalpatnam areas. The Karimnagar Granulite Terrane (KGT) showing up as a thin (about 10-15 km wide) north-south belt near Khammam, widens to about 100 km near Warangal and extends through Karimnagar, Adilabad and beyond up to Wardha in a NW-SE direction, parallel to the Godavari basin. The Bhopalpatnam Granulite Terrane (BGT) appears as a 10 km wide linear belt on the eastern side of the basin. The Eastern Ghat Granulite Terrane (EGT), which occupies a vast area along the east coast of India, also possesses similar characteristic features within the study area. About 15 km east of Hyderabad, a north-south linear belt showing characteristic signatures of granulites could be identified from the aeromagnetic image. The belt, named as the Hyderabad Granulite Terrane (HGT) is about 25 km wide and joins the KGT near Karimnagar. These granulite terranes show higher values of magnetic susceptibility and density (except that of HGT).

3 illus, 9 ref

001176   Amreek Singh;Ganju a;Vaidya S K (Snow & Avalanche Study Establ, , Manali, Himachal Pradesh, Email: amreek_s@hotmail.com) : Geohazard potential of snow avalanches in Western Himalaya. Bull Indian Geol Ass 2004, 37(1-2), 15-23.

Snow avalanches are known for their destructive potential. Though the event lasts for a few minutes only, it affects tens of hectares of area in no time. Keeping aside its destructive power, snow avalanche is a natural phenomenon of off-loading snow from slopes. However, they have far greater implications than mere visible destruction for which they are generally known. This aspect of avalanches has attracted attention in recent times. With the increased movement and habitation of mankind in mountainous regions, avalanche hazard needs to be studied afresh and comprehensively. While analysing the destruction caused by avalanches in northwestern Himalaya, discusses the effects of avalanches in general on other natural resources. Avalanches erode soil cover, initiate rock fall, expose slopes of its insulating snow cover, cause damming of rivers and destroy forests. However, mankind also knows this natural phenomenon for certain merits. The authors have addressed some gains of avalanches. Melting avalanche debris releases water to streams gradually. Soil and rock transport to streams by avalanches, is used by mankind for various purposes. The damming of rivers by avalanches may replenish aquifers. All this, of course, is available at the cost of damage, the avalanches cause to mankind in terms of lives and property. A balanced view of human interaction with avalanches is thus imperative to ensure safety and steady growth of mankind in mountains. In the end, the paper summarizes various techniques to mitigate the hazard posed by avalanches and discusses their merits and limitations from the point of view of environmental conservation of the area.

4 illus, 7 ref

001175   Ahmad S M;Dayal A M;Padmakumari V M;Babu G A; Gopalan K (Natn Geophys Res Inst, , Uppal Road, Hyderabad-500 007, Email: smasoodahmad@rediffmail.com) : Changes in seawater <. J Geol Soc India 2005, 65(2), 147-57.

A seawater ⁸⁷Sr/⁸⁶Sr record is generated for early Miocene to early late Miocene based on measurements of 114 samples of cleaned planktonic foraminifera from Ocean Drilling Program site 758 (Hole 758A) in the eastern Indian Ocean. Age model for this Site is based on nannofossil events and interpolated numerical ages are compared with Sr isotopically-derived ages. There is a fairly good agreement between the two stratigraphic tools (<60>±1.5 Ma). ⁸⁷Sr/⁸⁶Sr ratio during <126>23.7 Ma to <126>8.1 Ma increased from 0.70828 to 0.70895, with variations in the rate of ⁸⁷Sr/⁸⁶Sr increase. Seventh-order polynomial fit curve shows the ⁸⁷Sr/⁸⁶Sr increase rates of 44 x 10^-6 m.y^-1 for <126>23.7 to <126>19.2 Ma, 41 x 10^-6 m.y.^-1 for <126>18.2 to <126>10.8 Ma, and 25 x 10^-6 m.y.^-1 for <126>10.8 to <126>8.1 Ma. These rates are broadly consistent with the growth rates of ⁸⁷Sr/⁸⁶Sr reported from other DSDP and ODP sites with some minor differences. A composite Sr isotope curve constructed for the 24-8 Ma is broken into three linear segments with a different linear regression equation. The overall rate of ⁸⁷Sr/⁸⁶Sr increase for <126>24-8 Ma at site 758A (40 x 10^-6 m.y.^-1) is in agreement with the rate of ⁸⁷Sr/⁸⁶Sr increase of the composite curve (42 x 10^-6 m.y^-1).

6 illus, 33 ref

001174   Ahmad A H M;Sayeed A S M;Khan A F;Saikia C (Dep of Geol, Aligarh Muslim Univ, Aligarh-202 002) : Environmental interpretation of grainsize and provenance of the sandstones of lameta formation (Cretaceous), Jabalpur area, Madhya Pradesh. Indian J Petrol Geol 2004, 13(2), 87-93.

Lameta Formation crop out as isolated patches along the Narmada Rift basin in the Jabalpur area in the state of Madhya Pradesh. The sandstones are generally fine to coarse grained, poorly to well sorted, coarse to strongly skewed, very platykurtic to leptokurtic. The sand grains are very angular to well rounded. Most of the studied grains show low spherecity and sandstones are immature to submature. Bimodality along with the presence of extensive burrows in the sandstones and ooids in the overlying limestones of Lameta Formation reflect that the sediments were deposited in beach/shol environment. On the basis of present day distribution of Precambrian rock types in combination with detrital mineralogy of the sandstones, it may be inferred that most of the Cretaceous sediments was derived from meta sedimentary rocks and granite - gneisses of Mahakoshal Group.

3 illus, 19 ref

001173   Ahmad A H M;Alam M M;Khan M H A (Dep of Geol, Aligarh Muslim Univ, Aligarh-202 001) : Petrofacies and diagenesis of bayana basin conglomerates (Delhi supergroup), Bharatpur district, Rajasthan. J Geol Soc India 2005, 65(3), 335-45.

The Bayana Sub-basin comprises thick sequence of metavolcanics and metasedimentary rocks belonging to Delhi Supergroup. The deposition of sediments took place in response to vertical tectonism during Middle Proterozoic in fluvial and shallow marine environments. The rocks are mainly elastics and include conglomerate, sandstone and shale. The conglomerate lithofacies and petrofacies were studied with, a view to understand the tectonic setting of the provenance and the basin. The conglomerate matrix consist of framework detrital grains such as several varieties of quartz followed by rock fragments, mica, feldspar, and heavy minerals. The Qt-F-L, Qm-F-Lt, Qp-Lv-Ls and Qm-P-K diagrams suggest continental block, recycled orogen provenance, rifted continental margin type of basin setting and overall maturity and stability of the continental block provenance. The cement phases in conglomerate matrix consist of iron oxide, silica, carbonate and barite. Dominance of floating, point and long contacts indicates that the sand grains did not suffer much pressure solution.

16 illus, 6 tables, 15 ref

000354   Sukhija B S;Gupta H (Natn Geophys Res Inst, , Uppal Road, Hyderabad-500 007) : Paleoseismicity and recurrence of large/great earthquakes in shillong plateau, India. Himalayan Geol 2005, 26(1), 187-92.

Paper reviews the first ever directly estimated recurrence period of large/great earthquakes from the Himalayan region, based on extensive paleoseismological measurements from ten trenches and ¹⁴C dating of twenty five organic samples associated with the seismites in the Shillong Plateau encompassed by the meizoseismal area of the great 1897 Assam earthquake. Analysis of paleoliquefaction data and chronology of paleoseismic events provide evidence for three great paleoseismic events besides the 1897 event, which occurred during 1450-1650 AD, 700-1050 AD and the third one pre-dates 600 AD. These results provide a recurrence period of 400-600 years for great earthquakes in the Shillong Plateau.

4 illus, 1 table, 27 ref

000353   Srivastava R K;Sinha A K (Igneous Petro Laboratory Dep of Geol, Banaras Hindu Univ, Varanasi-221 005, Email: rajeshgeolbhu@yahoo.com) : Geochemistry and petrogenesis of early cretaceous sub-alkaline mafic dykes from Swangkre-Hongmil, East Garo hills, Shillong plateau, northeast India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 683-97.

Numerous early Cretaceous mafic and alkaline dykes, mostly trending in N-S direction, are emplaced in the Archaean gneissic complex of the Shillong plateau, northeastern India. These dykes are spatially associated with the N-S trending deep-seated Nongchram fault and well exposed around the Swangkre-Rongmil region. The petrological and geochemical characterstic of mafic dykes from this area are presented. These mafic dykes show very sharp contact with the host rocks and do not show any signature of assimilation with them. Petrographically these mafic dykes vary from fine-grained basalt (samples from the dyke margin) to medium-grained dolerite (samples from the middle of the dyke) having very similar chemical compositions which may be classified as basaltic-andesite/andesite. The geochemical characteristics of these mafic dykes suggest that these are genetically related to each other and probably derived from the same parental magma. Although, the high-field strength element (+rare-earth elements) composition disallow the possibility of any crystal involvement in the genesis of these rocks, but Nb/La, La/Ta, and Ba/Ta ratios, and similarities of geochemical characteristics of present samples with the Blan Bank basalts and Rajmahal (Group II) mafic dyke samples, suggest minor contamination by assmiliation with a small amount of upper crustal material. Chemistry, particularly REE, hints to the alkaline basaltic nature of melt. Trace element modelling suggests that the melt responsible for these mafic dykes had undergone extreme differentiation (<126> 50%) before its emplacement. The basaltic/andesite nature of these rocks may be attributed to this differentiation. Chemistry of these rocks alsos indicates <126> 10-15% melting of the mantle source. The mafic dyke samples of the investigation show very close geochemical similarities with the mafic rocks derived from the Kerguelen mantle plume. Perhaps the Swangkre-Rongmil mafic dykes are also derived from the Kerguelen mantle plume.

11 illus, 3 tables, 63 ref

000352   Srivastava R K;Chandra R;Shastry A (Igneous Petro Laboratory Dep of Geol, Banaras Hindu Univ, Varanasi-221 005) : High-Ti type N-MORB parentage of basalts from the south Andaman ophiolite suite, India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 605-18.

A complete dismembered sequence of ophiolite is well exposed in the south Andaman region that mainly comprises ultramafic cumulates, serpentinite mafic plutonic and dyke rocks, pillow lava, radiolarian chert, and plagiogranite. Pillow lavas of basaltic composition occupy a major part of the Andaman ophiolite suite (AOS). These basalts are well exposed all along the east coast of southern part of the south AOS. Although these basalts are altered due to low-grade metamorphism and late hydrothermal processes, their igneous textures are still preserved. These basalts are mostly either aphyric or phyric in nature. Aphyric type exhibits intersertal or variolitic textures, whereas phyric variety shows porphyritic or sub-ophitic textures. The content of alkalies and silica classify these basalts as sub-alkaline basalts and alkaline basalts. A few samples show basaltic andesite, trachy-basalt, or basanitic chemical composition. High-field strength element (HFSE) geochemistry suggests that studied basalt samples are probably derived from similar parental magmas. Al₂O₃/TiO₂ and CaO/TiO₂ ratios classify these basalts as high type basalt. On the basis of these ratios and many discriminant functions and diagrams, it is suggested that the studied basalts, associated with Andaman ophiolite suite, were derived from magma similar to N-MORB and emplaced in the mid-oceanic ridge tectonic setting.

9 illus, 2 tables, 42 ref

000351   Sinha R;Tandon S K;Gibling M R;Bhattacharjee P S;Dasgupta A S (Engng Geosciences Div, Indian Inst of Technol, Kanpur-208 018) : Late quaternary geology and alluvial stratigraphy of the Ganga basin. Himalayan Geol 2005, 26(1), 223-40.

The Ganga basin in the Himalayan foreland is a part of the world's largest area of modern alluvial sedimentation and supports a population of over 200 million people. The Ganga plain deposits not only provide a modern analogue for the ancient fluvial sequences of the Himalayan foreland basin but they also provide one of the most significant continental records for understanding the interplay of climate, tectonics and eustatic changes in generating thick sedimentary fills in a monsoon-dominated foreland system. Given the large dimensions of the Ganga basin and the lack of an integrated approach, the available data are fragmentary, and several important questions regarding the sedimentary architecture and the process-form relationships of the parent rivers remain unanswered. The paper reviews the available information on the near-surface Late Quaternary stratigraphy of the upper, middle and lower Ganga basin, and reports new results based on studies of river cliff sections and shallow boreholes down to <126>50 m depth. Authours has recorded significant variation in sedimentary architecture between the upper and middle Ganga plains in the western and eastern parts of the basin, respectively. This variation reflects geomorphic diversity (linked especially to precipitation gradients) and tectonic history in the frontal erogenic areas which, in turn, impact sediment supply into the basin. Many of the alluvial sequences in the upper Ganga basin are interrupted by discontinuities that probably reflect Quaternary climatic fluctuations. In addition to controlling the long-term accumulation rate, tectonics may have had some local influence, and the effects of eustatic changes were almost certainly limited to the deltaic region of the lower Ganga plains, extending to a maximum of 300-400 km landward.

7 illus, 108 ref

000350   Singh V S;Nandakumar M V;Sarma M R K;Dimri V P (NO, Natn Geophys Res Inst, Hyderabad-500 007, Email: vssingh77@hotmail.com) : Changes in groundwater regime at Neill Island (South Andaman) due to earthquake and tsunami of 26 December 2004. Curr Sci 2005, 88(12), 1984-7.

The earthquake and tsunami of 26 December 2004 have caused vast devastation to human life and property. It has been severe in the Andaman and Nicobar Islands, particularly the Nicobar Islands. The earthquake has caused subsidence of land at some places and up-liftment at other places in many islands. Groundwater, which is only source of drinking water at some of the tiny islands, has been affected due to tsunami. Neill Island is one such island in South Andaman. Results of hydro-geological investigation before and after the earthquake and tsunami of 26 December 2004 have been presented.

9 illus, 1 ref

000349   Singh S (Earth Sci Dep, Indian Inst of Technol Roorkee, Roorkee-247 667, Email: sandpfes@iitr.ernet.in) : U-Pb ages from Himalayan collisional belt. Himalayan Geol 2005, 26(1), 61-76.

The ages obtained from the Himalayan Collisional Belt have been constrained from both Rb-Sr and U-Pb dating techniques. However, the main component of data generated is from Rb-Sr systematics and as compared to this only a few ages are being reported by U-Pb technique. U-Pb dating technique on different accessory mineral is used for the determination of high precision mineral growth ages in igneous and metamorphic rocks. The major reasons for their use are to obtain high precision ages from zircon and the resistance of this mineral to thermal disturbance. Analyses can be performed by isotopic dilution technique on Thermal Ionization Mass Spectrometer (TIMS) or insitu measurement on Secondary Ionmicroprobe Mass Spectrometer (SIMS) and Laser Ablation -Multicollector-Inductively Coupled Plasma Mass Spectrometer (LA-MC-ICP-MS). To understand the geodynamics of the Himalayan Collision Zone over the years there is significant progress towards U-Pb geochronology. However, the data published mainly constrain the ages which are either few pre-Himalayan mainly Pan-African or majorities are syn- to post-Himalayan. There is still need of generating more precise data on geochronometry from Himalayan Collision Zone for better understanding of the geodynamics of the Himalaya.

^iia4 illus, 1 table, 142 ref

000348   Singh K K (National Centre for Medium Range Weather Forecasting, DST, , New Delhi-110 003) : Drought preparedness and mitigation. J Indian Soc Agric Statist 2003, 56(1), 95.

000347   Singh A P;Kumar N;Singh B (Natn Geophys Res Inst, , Uppal Road, Hyderabad-500 007, Email: apsingh_ngri@yahoo.com) : Magmatic underplating beneath the rajmahal traps: gravity signature and derived 3-D configuration. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 759-69.

The early Cretaceous thermal perturbation beneath the eastern continental margin of the Indian shield resulted in the eruption of the Rajmahal Traps. To understand the impact of the magmatic process that originated in the deep mantle on the lower crustal level of the eastern Indian shield and adjoining Bengal basin the conspicuous gravity anomalies observed over the region have been modelled integrating with available geophysical information. The 3-D gravity modelling has delineated 10-15 km thick high-density (ρ = 3.02g/cm³) accreted igneous layer at the base of the crust beneath the Rajmahal Traps. Thickness of this layer varies from 16 km to the west of the Rajmahal towards north to about 12 km near Kharagpur towards south and about 18km to the east of the Raniganj in the central part of the region. The greater thickness of the magmatic body beneath the central part of the region presents itself as the locus of the potential feeder channel for the Rajmahal Traps. It is suggested that the crustal accretion is the imprint of the mantle thermal perturbation, over which the eastern margin of the eastern Indian shield opened around 117 Ma ago. The nosing of the crustal accretion in the down south suggests the possible imprint of the subsequent magmatic intrusion along the plume path.

5 illus, 44 ref

000346   Singh A K;Vallinayagam G (Wadia Inst of Himalayan Geol, Northeast Unit, Vivek Vihar, Itanagar-791 113, Email: kk_luwang@rediffmail.com) : Geochemistry and petrogenesis of anorogenic basic volcanic-plutonic rocks of the Kundal area, Malani igneous suite, western Rajasthan, India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 667-81.

The Kundal area of Malani Igneous Suite consists of volcano-plutonic rocks. Basalt flows and gabbro intrusives are associated with rhyolite. Both the basic rocks consist of similar mineralogy of plagioclase, clinopyroxene as essential and Fe-Ti oxides as accessories. Basalt displays sub-ophitic and glomeroporphyritic textures whereas gabbro exhibits sub-ophitic, porphyritic and intergrannu lar textures. They show comparable chemistry and are enriched in Fe, Ti and incompatible ele ments as compared to MORB/CFB. Samples are enriched in LREE and slightly depleted HREE patterns with least significant positive Eu anomalies. Petrographical study and petrogenetic modeling of [Mg]-[Fe], trace and REE suggest cogenetic origin of these basic rocks and they probably derived from Fe-enriched source with higher Fe/Mg ratio than primitive mantle- source. Thus it is concluded that the basic volcano-plutonic rocks of Kundal area are the result of a low to moderate degree (<60>30%) partial melting of source similar to picrite/komatiitic composition Within plate anorogenic setting for the basic rocks of Kundal area is suggested, which is in conformity with the similar setting for Malani Igneous Suite.

7 illus, 3 tables, 45 ref

000345   Sheth H C;Mathew G;Pande K;Mallick S;Jena B (Dep of Earth Sci, Indian Inst of Technol Bombay, Powai, Mumbai-400 076, Email: hcsheth@iitb.ac.in) : Cones and craters on mount pavagadh, Deccan traps: Rootless cones?. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 831-38.

Rootless cones, also (erroneously) called pseudocraters, form due to explosions that ensue when a lava flow enters a surface water body, ice, or wet ground. They do not represent primary vents connected by vertical conduits to a subsurface magma source. Rootless cones in Iceland are well studied. Cones on Mars, morphologically very similar to Icelandic rootless cones, have also been suggested to be rootless cones formed by explosive interaction between surface lava flows and ground ice. Reports a group of gentle cones containing nearly circular craters from Mount Pavagadh, Deccan volcanic province, and suggest that they are rootless cones. They are very similar morphologically to the rootless cones of the type locality of Myvatn in northeastern Iceland. A group of three phreatomagmatic craters was reported in 1998 from near Jabalpur in the northeastern Deccan, and these were suggested to be eroded cinder cones. A recent geophysical study of the Jabalpur craters does not support the possibility that they are located over volcanic vents. They could also be rootless cones. Many more probably exist in the Deccan, and volcanological studies of the Deccan are clearly of value in understanding planetary basaltic volcanism.

6 illus, 28 ref

000344   Shekhar M S;Dash S K (Cent for Atmospheric Sci, Indian Inst of Technol Delhi, Hauz Khas, New Delhi-110 016, Email: shekar@cas.iitd.ernet.in) : Effecct of Tibetan spring snow on the Indian summer monsoon circulation and associated rainfall. Curr Sci 2005, 88(11), 1840-4.

The effect of Tibetan snowfall in the month of April on the Indian summer monsoon circulation and associated seasonal rainfall has been examined using the Regional Climate Model version 3. This model has been integrated at 55km horizontal resolution from April to September in each of the years from 1993 to 1996. NIMBUS-7 SMMR snow depth data have been used as boundary conditions. Sensitivity experiment shows that Tibetan snow results in weak lower level monsoon westerlies and upper level easterlies. Without any initial snow, the sensible heat flux is found to be more, whereas with snow, the latent heat flux is more over the Tibetan region. Results indicate that the Indian Summer Monsoon Rainfall is reduced over entire India and its five homogeneous zones, when 10 cm of snow has been introduced over the Tibetan region in the preceding month of April. Quantitatively, rainfall decreases by 30% for all India, 23% for northwest India, 20% for west central India, 25% for central northeast India, 30% for northeast India and 15% for south peninsular India.

4 illus, 12 ref

000343   Sharma R S (Dep of Geol, Univ of Rajasthan, Jaipur-302 004) : Metamorphic history of the Himalayan rocks and a new model for the inverted metamorphism. Himalayan Geol 2005, 26(1), 19-24.

Renewed attention is drawn on metamorphism of the Himalayan rocks, especially on (i) nature of the basement of its sedimentry sequences, (ii) imprint of a Pre-Himalayan tectno-thermal event, if any, and (iii) inverted metamorphism associated with the Himalayan orogeny. A geodynamic model is proposed, linking the twin problem of southern convexity and inversion of metamorphic isograds that characterize this Tertiary fold belt all along its length.

14 ref

000342   Sharma R (Wadia Inst of Himalayan Geol, , Dehra Dun, Email: rajesh_fluid@rediffmail.com) : Fluid processes during sulphide mineralization in sedimentary succession of lesser Himalaya. Himalayan Geol 2005, 26(1), 77-83.

One or more of galena, sphalerite, chalcopyrite and pyrite are found at a number of locations associated with siliciclastic or carbonate host rocks of Lesser Himalaya. These host rock-ore assemblage with distinct field and textural features can be identified on a regional scale. Fluid inclusion microthermometry has been performed on the coeval gangue minerals which include quartz, calcite and dolomite. Fluid types in the mineralized vein quartz and siliciclastic (±basic metavolcanic) host rocks include early aqueous-carbonic and late aqueous-saline fluid. During the mineralization event immiscibility of the H₂O-CO₂ fluid phases occurred wherein density of the carbonic fluid was moderate. Incursion of early carbonic fluid refers to the emplacement of the associated metavolcanics. The mineralizing fluid of the sulphides in the carbonate host rocks was aqueous - moderate saline with temperatures generally <60> 200°C. Their Th vs Tm/ salinity plots and pairing of such data advocate that mixing of the two fluids occurred in the genesis of these sulphides; one most likely basinal brine and other a low salinity/temperature meteoric fluid.

5 illus, 23 ref

000341   Sharma K (Dep of Geol, Government Postgrad Coll, Sirohi-307 001, Email: sharmasirohi@yahoo.com) : The neoproterozoic malani magmatism of the northwestern Indian shield: Implications for crust-building processes. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 795-807.

Malani is the largest event of anorogenic felsic magmatism (covering <126> 50,000 km²) in India. This magmatic activity took place at <126> 750 Ma post-dating the Erinpura granite (850 Ma) and ended prior to Marwar Supergroup (680 Ma) sedimentation. Malani eruptions occurred mostly on land, but locally sub-aqueous conditions are shown by the presence of conglomerate, grits and pillow lava. The Malani rocks do not show any type of regional deformation effects. The Malanis are characterised by bimodal volcanism with a dominant felsic component, followed by granitic plutonism and a terminal dyke phase. An angular unconformity between Malani lavas and basement is observed, with the presence of conglomerate at Sindreth, Diri, and Kankani. This indicates that the crust was quite stable and peneplained prior to the Malani activity. Similarly, the absence of any thrust zone, tectonic melange and tectonised contact of the Malanis with the basement goes against a plate subduction setting for their genesis. After the closure of orogenic cycles in the Aravalli craton of the northwestern shield, this anorogenic intraplate magmatic activity took place in a cratonic rift setting under an extensional tectonic regime.

2 illus, 6 tables, 45 ref

000340   Sensarma S;Hoernes S;Mukhopadhyay D (Dep of Geol, St. Anthony's Coll, Shillong-793 001) : Relative contributions of crust and mantle to the origin of the bijli rhyolite in a palaeoproterozoic bimodal volcanic sequence (Dongargarh group), central India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 619-48.

New mineralogical, bulk chemical and oxygen isotope data on the Palaeoproterozoic Bijli Rhyolite, the basal unit of a bimodal volcanic sequence (Dongargarh Group) in central India, and one of the most voluminous silicic volcanic expressions in the Indian Shield, are presented. The Bijli Rhyolite can be recognized as a poorly sorted pyroclastic deposit, and comprises of phenocrystic K-feldspar + albite ± anorthoclase. set in fine-grained micro-fragmental matrix of quartz-feldsparsericite-chlorite-iron-oxide ± calcite. The rocks are largely metaluminous with high SiO₂, Na₂O + K₂O, Fe/Mg, Ga/Al, Zr, Ta, Sn, Y, REE and low CaO, Ba, Sr contents; the composition points to an 'A-type granite' melt. The rocks show negative Cs-, Sr-, Eu- and Ti- anomalies with incompatible element concentrations 2-3 times more than the upper continental crust (UCC). LREE is high (La/Yb <126> 20) and HREE 20-30 times chondritic. δ¹⁸O_whole-rock varies between 4.4 and 7.8%. (mean 5.87±1.26%.). The Bijli melt is neither formed by fractionation of a basaltic magma, nor does it represent a fractionated crustal melt. It is shown that the mantle-derived high temperature basaltic komatitic melts/high Mg basalts triggered crustal melting, and interacted predominantly with deep crust compositionally similar to the Average Archaean Granulite (AAG), and a shallower crustal component with low CaO and A1₂O₃ to give rise to the hybrid Bijli melts. Geochemical mass balance suggests that <126> 30% partial melting of AAG under anhydrous condition, instead of the upper continental crust (UCC) including the Amgaon granitoid gneiss reported from the area, better matches the trace element concentrations in the rocks. The similar Ta/Th of the rhyolites (0.060) and average granulite (0.065) vs. UCC (0.13) also support a deep crustal protolith. Variable contributions of crust and mantle, and action of hydrothermal fluid are attributed for the spread in δ¹⁸O_whole-rock values. The fast eruption of high temperature (<126> 900°C) rhyolitic melts suggests a rapid drop in pressure of melting related to decompression in an extensional setting.

14 illus, 7 tables, 78 ref

000339   Sensarma S;Hoernes S;Mukhopadhyay D (Dep of Geol, St. Anthony's Coll, Shillong-793 001) : Relative contributions of crust and mantle to the origin of the bijli rhyolite in a palaeoproterozoic bimodal volcanic sequence (Dongargarh group), central India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 619-48.

New mineralogical, bulk chemical and oxygen isotope data on the Palaeoproterozoic Bijli Rhyolite, the basal unit of a bimodal volcanic sequence (Dongargarh Group) in central India, and one of the most voluminous silicic volcanic expressions in the Indian Shield, are presented. The Bijli Rhyolite can be recognized as a poorly sorted pyroclastic deposit, and comprises of phenocrystic K-feldspar + albite ± anorthoclase. set in fine-grained micro-fragmental matrix of quartz-feldsparsericite-chlorite-iron-oxide ± calcite. The rocks are largely metaluminous with high SiO₂, Na₂O + K₂O, Fe/Mg, Ga/Al, Zr, Ta, Sn, Y, REE and low CaO, Ba, Sr contents; the composition points to an 'A-type granite' melt. The rocks show negative Cs-, Sr-, Eu- and Ti- anomalies with incompatible element concentrations 2-3 times more than the upper continental crust (UCC). LREE is high (La/Yb <126> 20) and HREE 20-30 times chondritic. δ¹⁸O_whole-rock varies between 4.4 and 7.8%. (mean 5.87±1.26%.). The Bijli melt is neither formed by fractionation of a basaltic magma, nor does it represent a fractionated crustal melt. It is shown that the mantle-derived high temperature basaltic komatitic melts/high Mg basalts triggered crustal melting, and interacted predominantly with deep crust compositionally similar to the Average Archaean Granulite (AAG), and a shallower crustal component with low CaO and A1₂O₃ to give rise to the hybrid Bijli melts. Geochemical mass balance suggests that <126> 30% partial melting of AAG under anhydrous condition, instead of the upper continental crust (UCC) including the Amgaon granitoid gneiss reported from the area, better matches the trace element concentrations in the rocks. The similar Ta/Th of the rhyolites (0.060) and average granulite (0.065) vs. UCC (0.13) also support a deep crustal protolith. Variable contributions of crust and mantle, and action of hydrothermal fluid are attributed for the spread in δ¹⁸O_whole-rock values. The fast eruption of high temperature (<126> 900°C) rhyolitic melts suggests a rapid drop in pressure of melting related to decompression in an extensional setting.

14 illus, 7 tables, 78 ref

000338   Saraswati P K (Dep of Earth Sci, IIT Bombay, Mumbai-400 076, Email: pratul@iitb.ac.in) : Survival of the Fittest: Some cross-disciplinary issues in palaeonotology. Himalayan Geol 2005, 26(1), 295-8.

Advancements in information technology and molecular biology will have a great impact in palaeontological research. Efforts are on to share enormous amount of global palaeontological information in a database of taxonomy, ecology and temporal and spatial distributions of different life forms. The focus of future research will be to use this data to address biosphere - environment relationships and the evolutionary dynamics of past life. The molecular biology, with the development of PCR technique, will give an insight to the understanding of phylogenetic relationships among living and fossil taxa. The search for well-preserved materials for molecular study will require a good understanding of taphonomic processes. The taphonomic appraisal of the stratigraphic record has become very important also because of the high resolution environmental analysis being attempted today. The need of quantitative approach and integration with other sciences are considered important for the survival of palaeontology.

11 ref

000337   Saini H S;Tandon S K;Mujtaba S A I;Pant N C (NO, Geol Surv of India, Faridabad-121 001, Email: sktand@nda.vsnl.net.in ) : Lake deposits of the northeastern margin of Thar Desert: Holocene(?) palaeoclimatic implications. Curr Sci 2005, 88(12), 1994-2000.

The understanding of past climates, particularly Holocene climate, changes in continental settings is significant for improving the predictive capability of models used for building future climate change scenarios. Continental sedimentary systems such as lake and river basins support large agricultural communities; even the desert margins support a substantial rural population. Therefore, understanding of the responses of these systems to future climate changes on decadal, century, and millennial scales needs to be strengthened in order to determine the varying limits of land, soil, water and vegetation resource structure on the demographic structure. In this context, the lake/pond deposits of the northeastern margin of Thar Desert along a rainfall gradient (200-600 mm) from west to east have been documented. The potential of the lake deposits and the associated sedimentary facies for the reconstruction of post-Last Glacial Maximum climate history is discussed, and the need for developing a chronological database on this important archive of continental Holocene climate is recognized.

4 illus, 2 tables, 26 ref

000336   Sachan H K;Mukherjee B K;Ahmad T (Wadia Inst of Himalayan Geol, , Dehra Dun, Email: himanshusachan@rediffmail.com) : Cold subduction of the Indian continental crust: evidence from tso-morari region, Ladakh, India. Himalayan Geol 2005, 26(1), 25-32.

The mantle pressure on crustal rock is very rare phenomena, which was noticed from Tso- morari region of Ladakh India. The rock of the TMC complex- eclogite preserves the evidence for mantle signature as a pressure vessels. It is found as boudin lenses hosted by para and ortho Gneisses. The essential minerals for Eclogite- Garnet and clinopyroxene and the carbonates association with silica signifies the deep penetration of Indian continental material below the Asian land mass. Among the carbonates, the Magnesite- quartz and later on Magnesite- coesite association remain stable through out the P-T path achieving max P of <62> 39 kbar and T <62> 750° C. The Prograde carbonate assemblages Mg- Qtz - Tlc along with blueschist assemblage Gt- Glu- Pg stable below P<60> 25 kbar and T <60> 500°C. The quartz in the core of the garnet having fluid value of <62><62> 450 ppm. The Peak metamorphism achieved by representative assemblages by Pg- Ky, Tlc- Ky, Co- dol- Mg indicates P <126> 39 kbar and T <126> 750°C supported by the fluid value <60> 450 ppm in geotherm of <126>7°C/ km. The preservation of such UHP assemblages indicates that the rocks become exhumed to the surface along a path by rapid and almost isothermal decompression. The presence of aragonite and dolomite was noticed at the peak metamorphic temperature and pressure condition. The same aragonite later on has been converted to Mg- rich calcite during retrograde metamorphism. The mineral assemblage Gt- chl- eld indicate further retrogrative stage at the pressure of 4-5 kbar and a temperature of <60> 500°C. The peak assemblages believe to be stable in UHP Eclogite passing through the blueschist facies and finally undergone the greenschist facies metamorphism. The Peak metamorphic association and fluid value demonstrates that the attainment of ultra high pressure metamorphism showed that the cold Indian continental margin fragments boosted at maximum strain rates and took the material greater than the depth of 120 km and which need to exhumed back the material at much- much faster than the subduction.

3 illus, 2 tables, 21 ref

000335   Roy N G;Sinha R (Engng Geosci Grp, Indian Inst of Technol, Kanpur-208 016, Email: rsinha@iitk.ac.in) : Alluvial geomorphology and confluence dynamics in the gangetic plains, Farrukhabad-Kannauj area, Utter Pradesh, India. Curr Sci 2005, 88(12), 2000-06.

Remote sensing images and topographic maps have been used to understand the geomorphic processes in parts of the Gangetic plains of Uttar Pradesh. Detailed geomorphic mapping suggests that the confluences of the Ganga-Ramganga-Garra rivers have moved both upstream and downstream during the last 30 years in response to river capture, local cut-offs and aggradation. There is a remarkable difference in the fluvial dynamics of this region compared to the eastern Gangetic plains from where rapid and frequent channel avulsions have been reported. No definite trend in the movement of the confluence points has been observed and the work departs from earlier suggestions of regional controls such as choking up of rivers due to sea-level rise or increased erosion in the catchment areas.

7 illus, 21 ref

000334   Roy A;Sarkar A;Jeyakumar S;Aggrawal S K; Ebihara M;Satoh H (Coal Wing, Geol Surv of India, DK-6, Sector-II, Salt Lake, Kolkata-700 091, Email: a_roy119@yahoo.com) : Late Archaean mantle metasomatism below eastern Indian craton: Evidence from trace elements, REE geochemistry and Sr-Nd-O isotope systematics of ultramafic dykes. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 649-65.

Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma, Sr_i <126> 0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; (ΣHREE)_N <126> 2-3 times chondrite, (Gd/Yb)_N <126> 1). The ε_Nd(t) values vary from +1.23 to -3.27 whereas δ¹⁸O values vary from +3.16%. to +5.29%. (average +3.97%.±0.75%.) which is lighter than the average mantle value. Isotopic, trace and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised by the fluid (± silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted, variable ε_Nd, low Sr_i(0.702) and low δ¹⁸O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the granitic crust which possibly originated due to the same thermal pulse.

11 illus, 2 tables, 77 ref

000333   Ray J S;Shukla P N (Phys Res Laboratory, , Navrangpura, Ahmedabad-380 009, Email: jsray@prl.ernet.in) : Trace element geochemistry of amba dongar carbonatite complex, India: Evidence for fractional crystallization and silicate-carbonate melt immiscibility. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 519-31.

Carbonatites are believed to have crystallized either from mantle-derived primary carbonate magmas or from secondary melts derived from carbonated silicate magmas through liquid immiscibility or from residual melts of fractional crystallization of silicate magmas. Although the observed coexistence of carbonatites and alkaline silicate rocks in most complexes, their coeval emplacement in many, and overlapping initial ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios are supportive of their cogenesis; there have been few efforts to devise a quantitative method to identify the magmatic processes. Mades an attempt to accomplish this by modeling the trace element contents of carbonatites and coeval alkaline silicate rocks of Amba Dongar complex, India. Trace element data suggest that the carbonatites and alkaline silicate rocks of this complex are products of fractional crystallization of two separate parental melts. Using the available silicate melt-carbonate melt partition coefficients for various trace elements, and the observed data from carbonatites, tries to simulate trace element distribution pattern for the parental silicate melt. The results of the modeling not only support the hypothesis of silicate-carbonate melt immiscibility for the evolution of Amba Dongar but also establish a procedure to test the above hypothesis in such complexes.

6 illus, 2 tables, 39 ref

000332   Raval U (Natn Geophys Res Inst, , Hyderabad-500 007) : Some issues for future deep continental studies. Himalayan Geol 2005, 26(1), 253-69.

12 illus, 85 ref

000331   Rashid S A (Dep of Geol, Aligarh Muslim Univ, Aligarh-202 002, Email: rashidamu@hotmail.com) : The geochemistry of mesoproterozoic clastic sedimentary rocks from the Rautgara formation, Kumaun lesser Himalaya: implications for provenance, mineralogical control and weathering. Curr Sci 2005, 88(11), 1832-6.

The Mesoproterozoic clastic sedimentary rocks, comprising pelites and quartzites from the Rautgara Formation, Kumaun Lesser Himlaya, have been analysed for major and trace elements, including Rare Earth Elements (REEs) to evaluate their provenance and weathering history. The pelitic rocks are characterized by moderate SiO₂ and A1₂O₃ contents and show consistent REE patterns with LREE (light REE)-enriched and HREE (heavy REE)-depleted patterns (La_N/Yb_N = 7.4-10.3). The total REE abundances of Rautgara pelites are high (up to 266 ppm) with large negative Eu-anomalies (Eu/Eu* = 0.57-0.64). Except high SiO₂ contents, the other major and trace element concentrations are significantly low in the associated quartzites. Although the quartzites contain low REE abundances (up to 41 ppm), their patterns, including negative Eu anomalies, are akin to pelites, suggesting that both the rock types be derived from similar source. The Chemical Index of Alteration and A-CN-K parameters indicate that moderate chemical weathering has taken place in the source region of the Rautgara rocks. The linear correlation coefficients between Al₂O₃, K₂O, TiO₂ and total REE reveal that the accessory minerals (mainly Ti-bearing phases) have hosted the REEs. The striking similarities between the REE patterns of Rautgara pelites and BGC of Aravalli and Bundelkhand granitoids, which are consistent with the palaeocurrent studies of the area, indicate that the granitoid rocks from these regions have supplied detritus to the Lesser Himalayan Rautgara sedimentary basin.

4 illus, 1 table, 30 ref

000330   Ramanamurty M V;Sundaramoorthy S;Pari Y;Rao V R;Mishra P;Bhat M;Usha T;Venkatesan R;Subramanian B R (Dep of Ocean Dev, Integrated Cstl and Mar Area Mgmt Project Directorate, Chennai-601 302) : Inundation of sea water in Andaman and Nicobar Islands and parts of Tamil Nadu coast during 2004 Sumatra tsunami. Curr Sci 2005, 88(11), 1736-40.

7 illus, 2 tables, 3 ref

000329   Rajkumar V;Siva Siddaiah N;Sangode S J; Kumaravel V;Juyal K P;Mathur N S (Wadia Inst of Himalayan Geol, , 33-General Mahadeo Singh Road, Dehra Dun-248 001) : Preliminary paleomagnetic results of the Kakara - Subathu in Dogadda area, Uttaranchal Himalaya. Himalayan Geol 2005, 26(1), 103-8.

Paleomagnetic results from 10 oriented sites collected from Kakara-Subathu Formations (Late Paleocene-Middle Eocene in Dogadda area, Uttaranchal are presented. Rock magnetic studies infer the predominance of single domain magnetite for Kakara Formation, while the terminal Kakara Formation and overlying Subathus (basal part) predominates hematite. Thermal and alternating field demagnetization methods are applied to clean the secondary components at around 500°C and <62> 40 mT respectively. Using mean directions for characteristic remanant magnetization, authors has calculates the apparent pole position of λp = 21.5°, φp = 19.1° for Kakara, and λp = -43.5°, φp = 106° for Subathu Formation. Based upon these preliminary results, author has reported a paleolatitude of -36.4° for the Kakara and -12.7° for the Subathu Formations in the study area.

6 illus, 1 table, 20 ref

000328   Rajesh H M;Santosh M (Dep of Geogrl Sci and Plan, Univ of Queensland St Lucia 4072, Queensland, Australia) : Charnockitic magmatism in southern India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 565-85.

Large charnockite massifs cover a substantial portion of the southern Indian granulite terrain. The older (late Archaean to early Proterozoic) charnockites occur in the northern part and the younger (late Proterozoic) charnockites occur in the southern part of this high-grade terrain. Among these, the older Biligirirangan hill, Shevroy hill and Nilgiri hill massifs are intermediate charnockites, with Pallavaram massif consisting dominantly of felsic charnockites. The charnockite massifs from northern Kerala and Cardamom hill show spatial association of intermediate and felsic charnockites, with the youngest Nagercoil massif consisting of felsic charnockites. Their igneous parentage is evident from a combination of features including field relations, mineralogy, petrography, thermobarometry, as well as distinct chemical features. The southern Indian charnockite massifs show similarity with high-Ba-Sr granitoids, with the tonalitic intermediate charnockites showing similarity with high-Ba-Sr granitoids with low K₂O/Na₂O ratios, and the felsic charnockites showing similarity with high-Ba-Sr granitoids with high K₂O/Na₂O ratios. A two-stage model is suggested for the formation of these charnockites. During the first stage there was a period of basalt underplating, with the ponding of alkaline mafic magmas. Partial melting of this mafic lower crust formed the charnockitic magmas. Here emplacement of basalt with low water content would lead to dehydration melting of the lower crust forming intermediate charnockites. Conversely, emplacement of hydrous basalt would result in melting at higher f_H2O favoring production of more siliceous felsic charnockites. This model is correlated with two crustal thickening phases in southern India, one related to the accretion of the older crustal blocks on to the Archaean craton to the north and the other probably related to the collision between crustal fragments of East and West Gondwana in a supercontinent framework.

10 illus, 132 ref

000327   Rajendra Prasad B;Vijaya Rao V (Natn Geophys Res Inst, , Hyderabad-500 007, Email: rajbitragunta@yahoo.com) : Seismic imaging of Indian continental crust. Himalayan Geol 2005, 26(1), 125-38.

The reflection studies have provided reliable seismic images of the deep crust and subcrustal lithosphere leading to a new insight into the complex structures involved in the regions. The seismic images provided useful inputs to understand the complex geodynamie processes responsible for the evolution of the important tectonic blocks of the Indian shield. A good correlation is found between the surface features and subsurface reflection geometry. The nature, dimension and geometry of reflection bands extending to various crustal depths up to Moho in the study regions indicate compressional environment involving thick-skinned tectonics were responsible for their development. Signatures of paleo-subduction, collision and suture zones are well identified by the seismic images. The reflection fabric provides a unique geophysical framework to understand the rheological structure of the paleo-subduction / collision zones.

11 illus, 39 ref

000326   Rajasekhar R P;Mishra D C (NO, Natn Geophys Res Inst, Hyderabad-500 007, Email: dcm_ngri@yahoo.co.in) : Analysis of gravity and magnetic anomalies over Lonar lake, India: an impact crater in a basalt province. Curr Sci 2005, 88(11), 1836-40.

The amplitude and circular/semi-circular nature of gravity and magnetic anomalies of 2.5 mGal and 550 nT respectively, in the case of Lonar lake are similar to those reported over impact craters. Analysis of these anomalies suggests that the impact has modified the magnetization vector and density of the country rock (Deccan trap) up to about 500-600 m below the surface with a brecciated part of about 135 m of bulk density of 2.60 g/cm³ and fragmented layer of about 150 m of bulk density 2.7 g/cm³ with induced magnetization. The affected part depth-wise is approximately 0.3-0.35 times the diameter of the crater, as is found in the case of impact craters the world over. The impact has re-magnetized this region in the present-day earth's magnetic field, demagnetizing the remanent magnetization of the Deccan trap. This implies that the temperature on impact must have been raised above 550 °C corresponding to Curie point of magnetite. Part of the brecciated zone showing very high susceptibility of about 4.0 x 10^-3 SI units, suggests concentration of magnetite in this part which may represent parts of meteorite embedded there. This approach may help in the analysis of magnetic and gravity fields due to impact craters of celestial bodies with exposed trap rocks, such as the Moon, Mars, etc.

4 illus, 20 ref

000325   Raina V K (NO, , 258, Sector-17, Punchkula-134 109, Haryana) : Glacier studies in India. Himalayan Geol 2005, 26(1), 285-93.

Paper deals with the glaciological studies carried out in Indian part of the Himalaya by the Geological Survey of India. It includes distribution of glaciers, glacier inventory, mass balance studies, glacial hydrometry, glacial melt water discharge and sediment transport, glacier thickness, glacial geomorphology, thermal profiling and dating of glacial ice.

6 illus, 3 tables, 17 ref

000324   Rai H (Wadia Inst of Himalayan Geol, , 33, General Mahadeo Singh Road, Dehradun-248 001, Email: hakimrai2@rediffmail.com) : Ophiolite sequence in the indus suture zone of the Eastern Ladakh, India. Himalayan Geol 2005, 26(1), 41-7.

A characteristic feature of the melange in the eastern Ladakh is the occurrence of a large fragment of oceanic crust. Exposure lies to the south of Nidar village on the Indus Suture zone. It represents a complete ophiolite sequence and is constituted of peridotite, dunite, pyroxenite, serpentinite, gabbro, sheeted dykes, pillow lava, and pelagic sediments. Presence of these rocks in a single unit make it comparable with any well known ophiolite sequence formed at mid-oceanic ridge due to sea-floor spreading process. Successively, flysch is deposited over the pelagic sediments covering the pillow lava. Deposition of the Indus Formation suggest a transition stage from submarine to continental conditions as a consequence of collision which was initiated during the late phase of flysch deposition. The Kargil and Liyan molasse were deposited in separate intermontane fore-arc basins during the culmination of orogeny. Sequentially development of south handing thrust started in syn- and post intermontane basin formation period.

1 illus, 28 ref

000323   Radhakrishna T;Joseph M (Cent for Earth Sci Stud, , Trivandrum-695 031, Email: tradhal@rediffmail.com) : Palaeomagnetism of mafic dykes and thermal history of the South Indian shield. Himalayan Geol 2005, 26(1), 151-60.

Mafic dykes, owing to strong magnetization signatures that can be easily measured in the laboratory, are the potential source of palaeomagnetic directional and pole data, particularly for the Precambrian Eon. At the same time, the thermal demagnetization data may provide useful information about the nature and extent of latter thermal influences subsequent to their emplacement. All the major cratons have witnessed episodic dyke magmatism (or other plutonic units and volcanic eruptions) since early Palaeoproterozoic till late Cretaceous Deccan eruptions. Thus the early Precambrian dykes may possess signatures of the latter thermal heating. Enhanced heat flow due to large-scale thermal influence of Deccan/Rajmahal eruptions has been recognized from the palaeomagnetic investigations of Vindhyan and Gondwana formations. Sufficient palaeomagnetic data are not available to evaluate this aspect from the other cratonic regions in India and therefore, authors has attempted to analyse the palaeomagnetic results on dykes of south India to asses the thermal influences in the region. Authors has observed that the thermal influence and related heat flow corresponding to the Deccan or other Cretaceous activity have no significant effects in the south Indian shield. However, the analysis could decipher a clear late Neoproterozoic thermal influence in the dykes from granulite region of Dharmapuri, Tiruvannamalai and Agali- Coimbatore areas, which are within or in close vicinity of Bhavani shear zone. Further, the analysis, in the light of recent data, suggest that a 1.0 Ga thermal event (suggested earlier) might not have a major influence in the Dharwar craton or in the granulite region of south India. The palaeodirections, which was earlier considered to be of 1.0 Ga, possibly correspond to Palaeoproterozoic intrusions. It is likely that the terrain has undergone large thermal influence due to late Palaeoproterozoic (1.65 Ga) dyke magmatism. More work is needed to establish the nature and extent of this thermal influence.

8 illus, 26 ref

000322   Pant R K;Phadtare N R;Chamyal L S;Juyal N (NO, Wadia Inst of Himalayan Geol, 33 General Mahadeo Singh Road, Dehra Dun-248 001, Email: phadtarenr@wihg.res.in) : Quaternary deposits in Ladakh and Karakoram Himalaya: a treasure trove of the palaeoclimate records. Curr Sci 2005, 88(11), 1789-98.

Preliminary observations on the Quaternary deposits of Ladakh and Karakoram Himalaya and their palaeoclimatic significance are highlighted in this article. Based on the geomorphology and sedimentary field evidences, a tentative scenario of landscape evolution and climate is proposed. The observations suggest that the Quaternary landscape was evolved due to the interaction of climate and seismicity. The earliest event was dominated by regional glacial activity that was followed by humid fluvio-lacustrine environments. This phase was succeeded by a renewed phase of glacial activity, though restricted to higher altitudes due to moisture-starved condition. Following this the region experienced marginal improvement in aridity that continued till present. The landform diversity and Quaternary deposits provide an opportunity to undertake a multidisciplinary approach for reconstructing the history of Quaternary climate and seismicity in the region.

9 illus, 78 ref

000321   Pande K;Pattanayak S K;Subbarao K V; Navaneethakrishnan P;Venkatesan T R (Planetary and Geosciences Div, Phys Res Laboratory, Navrangpura, Ahmedabad-380 009) : <. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 755-8.

It is reported a ⁴⁰Ar-³⁹Ar age of 66.0±0.9 Ma (2σ) for a reversely magnetised tholeiitic lava flow from the Bhimashankar Formation (Fm.), Giravali Ghat, western Deccan province, India. This age is consistent with the view that the 1.8-2km thick bottom part of the exposed basalt flow sequence in the Western Ghats was extruded very close to 67.4 Ma.

2 illus, 1 tables, 28 ref

000320   Naqvi S M (Natn Geophys Res Inst, , Hyderabad-500 007) : Mantle plumes, accretion - collision processes and the orogenic gold deposits with special reference to the Indian plate. Himalayan Geol 2005, 26(1), 139-42.

Large lode gold deposits associated quartz-carbonate veins are classified as orogenic gold deposits. These deposits are found in most of the orogens from Neoarchaean to Cenozoic. The identification of paleo-orogens or ancient orogens and fossil plumes have lead to new discoveries of the gold deposits. Irrespective of time and space constraints the gold deposits are formed under suitable P-T-t-d and f conditions.

^iia10 ref

000319   Nanda A C;Sehgal R K (Wadia Inst of Himalayan Geol, , Dehra Dun-248 001) : Recent advances in palaeontologic and magnetostratigraphic aspects of the Siwalik group of Northwestern Himalaya. Himalayan Geol 2005, 26(1), 93-102.

The Siwalik Group of northwestern India has yielded rich mammalian fauna in the last four decades and palaeontologic and stratigraphic (including magnetostratigraphic) studies have been confined mainly to Jammu, Nurpur and Bilaspur (Himachal), and Chandigarh regions. The Lower Siwalik Subgroup of Ramnagar, Jammu, comprising mainly red mudstones and grey sandstones, has yielded rich Chinji Fauna (Astarcian) and 36 species (including 10 marker species) are collected from this area. However, near Nurpur (Kangra, Himachal Pradesh) similar lithology has yielded Dhok Pathan Fauna (Turolian). This shows that red mudstones, generally considered characteristic of the Lower Siwalik Subgroup, are time transgressive. Multistoried sandstone bodies, which are considered characteristic of the Middle Siwalik Subgroup, have yielded typical Pinjor Fauna near Paonta. One of the most significant recent advancement in the study of the Upper Siwalik Subgroup is the recognition of the pre-Pinjor beds (referred to Tatrot/Saketi/Dhamala/Masol formations), in the type area of the Pinjor Formation of Chandigarh. In this region, different workers noted several faunal discrepancies concerning the Tatrot and Pinjor faunas. These are now attributed to the presence of a transitional zone between the pre-Pinjor and Pinjor beds of the Upper Siwalik Subgroup and also to time transgressive nature of lithology in certain sections. Magnetostratigraphic studies of the fossiliferous areas are limited and are carried out in Haritalyangar, Bilaspur and Nurpur, Kangra (Middle Siwalik Subgroup), and Jammu and Chandigarh regions (Upper Siwalik Subgroup). It is found that at Haritalyangar the referred Lower Siwalik Subgroup actually belongs to the Middle Siwalik Subgroup. Magnetostratigraphic study of the Siwalik succession of Nurpur supports an age equivalent to that of the Dhok Pathan Fauna. The type section of the Pinjor Formation is dated 2.58 to 0.63 Ma. Tatrot/Pinjor faunal break both in Jammu and Chandigarh regions coincides with the Gauss/Matuyama magnetic boundary and is dated at 2.58 Ma. The contact between the Pinjor and Boulder Conglomerate formations is time transgressive and ranges from 1.77 Ma to 0.6 Ma in different sections of Jammu and Chandigarh. On the basis of combined palaeontologic and magnetostratigraphic studies, two biostratigraphic interval-zones, Elephas planifrons Interval-Zone (3.6 to 2.6 Ma) and Equus sivalensis Interval-Zone (2.6 to 0.6 Ma), are recognized in Chandigarh region.

4 illus, 5 tables, 42 ref

000318   Muralidharan D;Rangarajan R;Murthy J V S; Prabhakar Rao Y (NO, Natn Biophys Res InstpHyderabad-500 007, , Email: muralidharan@ngri.res.in) : Mapping of hydrodynamic changes around radial arms of collector well by streaming potential survey. Curr Sci 2005, 88(12), 1901-04.

3 illus, 12 ref

000317   Mukul M (CSIR Cent for Math Modelling and Computer Simulation, , Bangalore-560 037) : Continental deformation and global positioning system based geodesy. Himalayan Geol 2005, 26(1), 193-8.

Global Positioning System (GPS) is a navigation and precise-positioning tool developed by the United State Department of Defense in 1973 primarily for military use. Subsequently, it was recognized that precise-positioning provided by GPS could be used in high-precision geodesy and for continental deformation studies to measure tectonic motions during and in between earthquakes particularly in strike-slip settings. Geodetic GPS measurements are accurate to a millimetre although vertical accuracies are still not up to the required level. GPS based geodesy has, therefore, provided additional insight into continental deformation over very short time scales. When integrated with deformation information obtained from structural geology (rocks), quaternary sediments (neotectonics) and earthquake data (seismotectonics), a better picture of the deformation kinematics emerges in both space and time. GPS measurements provide a fully dated, quantitative, deformation path which can be used to estimate seismic hazard better.

6 illus, 19 ref

000316   Mohan A (Dep of Geol, Banaras Hindu Univ, Varanasi-221 005, Email: amohanbhu@yahoo.com) : Nanoscience: A nanoscale revolution in earth sciences. Himalayan Geol 2005, 26(1), 281-4.

A revolution is taking place in science & technology in the emerging, interdisciplinary fields of nanoscience & technology -a revolution so profound that it is difficult to comprehend. Nanoscience is focused on the unique properties of nanoscale materials and devices, and the techniques that are used to synthesize, assemble and characterize such structures. In fact, their size is their advantage. It is predicted that nanotechnology will fundamentally transform science, technology and society. Geologists no longer have to focus only on the large scale processes that shape the earth but now they are using nanoscience to study Earth materials that play a vital role in Earth's sustainability. This is mainly because almost all geologic things are linked with the nanoscale phenomena.

16 ref

000315   Melluso L;Barbieri M;Beccaluva L (Dipartimento di Scienze della Terra, Universita di Napoli Federico II, via Mezzocannone 8, 80134 Napoli, Italy) : Chemical evolution, petrogenesis, and regional chemical correlations of the flood basalt sequence in the Central Deccan traps, India. Proc Indian Acad Sci-Earth Planet Sci 2004, 113(4), 587-603.

The lava sequence of the central-western Deccan Traps (from Jalgaon towards Mumbai) is formed by basalts and basaltic andesites having a significant variation in TiO₂ (from 1.2 to 3.3 wt%), Zr (from 84 to 253 ppm), Nb (from 5 to 16ppm) and Ba (from 63 to 407 ppm), at MgO ranging from 10 to 4.2 wt%. Most of these basalts follow a liquid line of descent dominated by low pressure fractionation of clinopyroxene, plagioclase and olivine, starting from the most mafic compositions, in a temperature range from 1220° to 1125°C. These rocks resemble those belonging to the lower-most formations of the Deccan Traps in the Western Ghats (Jawhar, Igatpuri and Thakurvadi) as well as those of the Poladpur formation. Samples analyzed for ⁸⁷Sr/⁸⁶Sr give a range of initial ratios from 0.70558 to 0.70621. A group of flows of the Dhule area, has low TiO₂ (l.2-1.5 wt%) and Zr (84-105 ppm) at moderate MgO (5.2-6.2 wt%), matching the composition of low-Ti basalts of Gujarat, low-Ti dykes of the Tapti swarm and Toranmal basalts, just north of the study area. This allows chemical correlations between the lavas of central Deccan, the Tapti dykes and the northwestern outcrops. The mildly enriched high field strength element contents of the samples with TiO₂ <62> 1.5wt% make them products of mantle sources broadly similar to those which generated the Ambenali basalts, but their high La/Nb and Ba/Nb, negative Nb anomalies in the mantle nor-malized diagrams, and relatively high ⁸⁷Sr/⁸⁶Sr, make evident a crustal input with crustally derived materials at less differentiated stages than those represented in this sample set, or even within the sub-Indian lithospheric mantle.

8 illus, 5 tables, 39 ref

000314   Manglik A (Natn Geophys Res Inst, , Uppal Road, Hyderabad-500 007) : Rheological modeling of the Indian continental lithosphere. Himalayan Geol 2005, 26(1), 165-73.

Flow and deformation of rocks strongly depend on the prevailing pressure and temperature conditions, composition and time scale of applied loading. At short time scales crust and mantle rocks mainly behave elastically whereas at large time scales viscous deformation prevails after a threshold pressure-temperature condition is exceeded. This property of change in the mode of deformation has been used to construct rheological models of lithosphere. For a continental lithosphere rheologically weak quartz - and feldspar-rich crust overlies a relatively strong olivine-rich sub-crustal lithosphere, giving rise to a stack of brittle and ductile layers within the continental lithosphere. Distribution of brittle and ductile layers in the lithosphere controls the mechanism of stress accumulation and failure and, thus, seismicity, and long term tectonic deformation. Therefore, an understanding of the rheological structure of lithosphere is required for studies related to earthquake mechanics and geo-tectonics. The article summarizes the work done on modeling of rheological structure of the Indian continental lithosphere and its implications on the deep crustal seismicity. Work done on the flexural modeling of the Indian continental lithosphere is also briefly covered.

5 illus, 1 table, 47 ref

000313   Mamtani M A;Arora B R (Dep of Geol & Geophysics, Indian Inst of Technol, Kharagpur-721 302) : Anisotropy of magnetic susceptibility - a useful tool for analyses of naturally deformed rocks. Himalayan Geol 2005, 26(1), 175-86.

In the paper, the application of Anisotropy of Magnetic Susceptibility (AMS) studies in the investigation of deformed-rocks is reviewed. AMS data from two different geological settings and lithounits are presented and discussed - one from the Precambrian quartzites and schists of the southern parts of Aravalli Mountain Belt and the other from the Banded Iron Formations of Bonai synclinorium, eastern India. The usefulness of AMS studies in (a) identifying weak late deformations, (b) strain analyses and (c) deciphering mechanism of folding is discussed. It is suggested that AMS is a versatile technique that can be applied for variety of structural geology problems such as study of deformed granites and their emplacement mechanisms, thrust tectonics and stress analyses related to neotectonic movements.

8 illus, 2 tables, 33 ref