Annual Report 1999-2000

Autonomous Institutions

Wadia Institute of Himalayan Geology, Dehradun

The Wadia Institute of Himalayan Geology is devoted to basic research in Himalayan Geology and its related fields, including crustal evolution, basin evolution, natural hazards, palaeoclimate, water resources and Himalayan geo-data base. The research activities of the Institute are conducted through timebound project mode and the areas of its multidisciplinary research are organised into six major research areas such as Structure & Tectonics, Igneous , Geochemistry & Petrology, Biostratigraphy, Sedimentology, Geomorphology & Environmental Geology & Geophysics. Highlights of research contributions made during the year 1999-2000 are summarised below :

Timing of India-Asia Collision Constrained on Micropaleontological Evidence

The study of biostratigrphic successions suggests that marine conditions commenced in Maastrichtian and continued till Early Lutetian during which the Kakara-Subathu succession was deposited. During deposition of the Subathu sediments, there was a minor regression of the Tethys in the early Late Ypresian times. The second and final regression took place in the Early Lutetian times. These two regressive phases are evidenced by biozones containing fresh to brackish water taxa, namely Seila, Physa, Aplexa and thin shelled oysters (molluscs); Neocypridis and llyocypris (ostracodes);and Chara fruits. The first regression is related to collision between the two plates, which resulted in uplift of the region in the early Late Ypresian times during which the beds of Cordiopsis subathooensis-Turritella subathooensis Zone were deposited. The second regression which took place in the Early Lutetian time (47 Ma) is attributed to uplift of the region due to continued collision between the two plates during which beds of Musculus muttali-Parinomya blanfordiana Zone were deposited.

Special emphasis was laid on preparation and identification of vertebrate remains recovered from the Murree Group of Kalakot area. The fossil material prepared includes a few rhinocerotoid teeth, an anthracotheriid jaw, an isolated rodent tooth, numerous crocodilian teeth, a varanid vertebra and several other postcranial elements of reptiles and mammals. The rodent tooth shows affinities with baluchimyines and primitive cricetids. The rhinocerotoids show similarities with amynodontids and paraceratheriinids.

Characterisation of Geologically Ancient River in Siwalik

Sedimentological, petrological and magnetostratigraphic studies carried out from the Ranital Kangra and Kotla sections of Kangra Valley infer that the sedimentation in the Kangra Sub-basin took place by east to west flowing Axial River System. A gradual fining trend noticed from east (Haritalyanagar) to west (Kotla) via Ranital (Center) areas and represents a single river deposition. Persistency of ferrugenous in the lower part (upto 415 m level) of the 2 km thick litho succession possibly suggests a warmer phase. The bulk mean low frequency initial volume susceptibility for Ranital-Kangra section is estimated 13.5x10e-11 and that of the Kotla section is 10.95 x 10e-11 depicting a rather weakly magnetic mineral assemblage. The sediments of Ranital-Kangra section shows a sudden peak of mass specific susceptibility at 1700 m level and thus suggesting a change in mineralogy.

Mid Oceanic Ridge Sediment of NeoTethys in Ladakh

Petrological investigations and x-ray diffraction of Nidar sediments show that radiolarian is commonly present in Chert and Jasperite and is generally in form of ooze and are generally filled with mosaic quartz. Pelagic facies shows dominance of quartz, feldspar and clay minerals. Tuff is generally of vitric type and also contains microlites as well as glass shreds. Presence of sanidine is few tuff indicates high temperature volcanic activity. Facies assemblage, geometry and petrographic investigation indicate complex array of depositional setting in mid oceanic ridge setting during formation of Nidar sedimentary member.

Early Form of Life in Geological Past

Microstromatolites and filamentous cyanobacteria have been discovered from Menga Limestone of Subansiri District, Arunachal Pradesh (Photograph 1). Microfacies analysis of microbial carbonates indicates that sedimentation is controlled by microbial activity.

Sponge spicules and Organic Walled Microfossils (OWM) from Gangolihat Dolomite has been discovered for the first time. The presence of Sponge spicules in the Calc Zone of Pithoragarh provides a firm evidence of metazoan silica biomineralisation in the fossil record from Neoproterozoic.

Structure Style of Kangra Reentrant

The geological and seismic data from the western Himalayan Foothills suggest that the Kangra reentrant is an oblique thrust ramp with prominent high lateral displacement. The oblique ramp was formed prior to the Tertiary Himalayan orogeny as listric normal fault, which later reactivated as thrust fault during the later compressional regime. In addition to the role of Inversion tectonics in the region, strike slip displacement along the reentrant and evidence of superposed deformation rules out the possibility of plane strain deformation.

Three additional balanced sections prepared from the western Himalayan foothills show variation in the shortening amounts from 22% to 71.3% over a distance of 400 km. The large variation can not be explained in the available tectonic models. The study suggests that the measured shortening amounts are geologically meaningless and the earthquake predictions based on the data are speculative. The data demand modifications in the technique of section restoration.

Deformation Features in the Main Central Thrust Zone

The Microstructural studies along the Main Central Thrust have been carried out along some of the major sections of the Garhwal Himalayas. This studies is primarily aim to understand grain scale mechanism operated concurrently or sequentially during its evolution. One of the most characteristics of the MCT is the common occurrence of inverted metamorphic sequence along the hanging wall. The quartzite dominated Berinag Thrust Sheet forms the foot walls the MCT. The present studies indicate internal deformation is not only restricted to the hanging wall but also along the foot wall the MCT. The microstructures like deformed lamellae, deformation band, ductile fracture planes, ribbon texture and polycrystalline quartz grains resulted from the dynamic recrystallization along the quartz clasts in the quartzite from the foot wall were observed. The mechanism broadly identified for these microstructures are intragranular fractures, low temperature ductile fracture and low temperature plasticity. Such processes operate under upper crustal conditions and it is envisaged for the evolution of the MCT.

Neotectonic Study in Sikkim

The Neotectonic studies in Sikkim Himalayas have revealed that there are evidences of crustal uplift characterized by left-, and right-, lateral faults high topographic relief as a result of recent uplift and potential site for the nucleation of earthquake. This N-S structure separates Kanchanjunga gneissic complex on its west and South Tibetan Detachment System (STDS) and migmatites, gneisses reworked granites and unconsolidated sediments of yardung - Galu Rift (YGR) on its east. The boundary of this structure consists of fault mylonite and majors and minor faults, silckensides and stretched mineral lineation which indicate northward movement of this structure. The Lithosphere geometry and prevalence of stresses at depth related to the volume of lithosphere subducted. This indicates that there are some pre-existing structures on the Indian continental margin before collision.

Eastern Syntaxis of Arunachal Pradesh

In the eastern Arunachal Pradesh mainly in the Lohit valley, the Lohit plutonic complex can be divided into two blocks, separated by Walong thrust. The western block comprises of hornblende diorite, gabbro intruded by dykes of andesite, basalt and microdiorite. This suit of igneous rock is intruded by soda rich biotite granodiorite of Trondjemitic affinity. This division of Lohit plutonic complex into two blocks (on the basis of field, petrography and geochemistry) has tremendous bearing towards understanding the tectonic evolution of this region.

Mineralogy of Chromite in Ladakh

The chromite in lowermost part of ultramafic zone occurs as pods and disseminated in dunite and harzburgite host rock in Nidar Ophiolitic sequence of Indus Suture Zone. The compositions of ore forming chromite in depleted mantle rock is uniform, showing high Cr-number (100 Cr/(Cr+Al)= 78-81) and Mg-number (100 Mg/(Mg+Fe)= 65-78) values.The primary silicate inclusion generally have high Mg number (>88-98) and are dominated by parasitic amphibole, olivine, diopside and enstatite suggesting that the melt responsible for crystallization of chromite have volatile rich fluid phase. The calculated parental melt compositions for chromite crystallization has Al203 10-07-10.75 (avg. 10.42) while FeO/MgO liquid ratio 0.4-0.98 (avg. 0.64). This parental melt composition indicates the chromite crystallizing melt was of boninitic in nature.

Stannoidite Mineralisation in Askote, Kumaun

Present study reports the occurrence of "stannoidite", a rare sulphide of Cu, Fe, Sn and some Zn, in Askot polymetallic sulphide assemblage. This brown stannite is earlier not known from the Himalayan mineral occurrences and is identified on the bases of recent ore chemical and petrographic studies. The stannoidite is found associated with chalcopyrite, cubanite, sphalerite, arsenopyrite and pyrite. This occurs as asymmetrical lamellae distributed irregularly within chalcopyrite and cubanite. The textural evidence, chemical data and experimental investigation of Cu-Fe-Zn-Sn-S system together indicate a temperature of formation of about 40-450oC for this mineralization. The exsolution texture wherein stannoidite occurs as myrmekitic intergrowth in chalcopyrite refers to their solid solution at high temperature and unmixing at about 450oC. Mineral assemblage with these species is known to occur in xenothermal and pyrometasomatic ore deposits.

Crustal Shortening Rate Using GPS

GPS measurements in NW Himalayas for crustal deformation studies have been initiated. Under a DST sponsored project more than 50 GPS stations have been installed in Himachal and Garhwal region. All the stations are properly monumented as per international standards, and documented. Two permanent GPS stations have been installed at Dehra Dun and Dharamsala, and have been continuously operating since Oct.’98. Velocity vectors obtained for the Dehra Dun network, relative to the Bangalore IGS station indicates that at least 15-20mm/yr crustal shortening is taking place between the Himalayan frontal zone and the stable Indian shield. Where and how exactly this 15-20mm/yr shortening is being accommodated is yet to be solved. Two possible suspects are the deformation in the foreland basin and crustal adjustment along the Narmada Son Lineament.

Pre- and Post Chamoli Earthquake Radon Measurements

Radon levels measured in the springs of Garhwal Himalayas before Chamoli earthquake (Mb=6.3) of 29th March 1999 have been compared with those measured immediately after the earthquake. Radon levels in springs are found to be affected by the earthquake. It was observed that in most of the springs, radon levels are increased after earthquake, particularly in worst effected area around Rudraprayag and Chamoli. However, radon concentrations were found to decrease in some springs. The enhancement or depletion of radon and water discharge may be attributed to the combined effect of earthquake and partial mobilization of major structural features and lithological control. A significant change in radon concentration and water discharge from springs in relation to earthquake shows that this technique may be exploited as an additional tool in earthquake prediction programme in Himalayan region.

Post-Chamoli Earthquake Survey

Macroseismic observation of Chamoli earthquake (Mb= 6.3) show that the maximum damage was concentrated in Chamoli town along the right bank of Alaknanda river upstream and between Chandrapuri and Cantha in Rudraprayag district. An isoseismal map prepared on the basis of damage survey shows NW-SE trend with major axis in the NW-SE direction and minor axis in NE-SW direction. The maximum intensity observed was VIII. An appreciable change in hydrological conditions has been noticed in a number of villages especially from meizo seismal zones. The maximum damage to building leads to greater loss of lives and property. According so the study the maximum damage to the building in Chamoli and Pipal Kothi etc. has been caused due to pounding effects. Due to the earthquake lot of wide and long land fissures have been developed with may lead to further loss to life and property specially to agricultural land in village between Chandra puri and Cantha Mandal region and in Gohna-Tal valley specially to Senji and Nijmula village.

Past Climate Signatures in Holocene Time

The paleoclimate data interpreted from the Dokriani peat pollen record revealed that Gangotri glacier had two prominent advances during the Holocene (i.e. past 10,000 yr). The first and most prominent glacial advance (termed as Shivling Glacier Advance) took place around 4000 - 3500 cal yr BP. The second one (Bhujbas Glacier Advance) which was less conspicuous, occurred around 800 cal yr BP, possibly corresponds with the Little Ice Age event in the Himalayas.

Radiogenic Isotope Laboratory

A Multi-collector Solid Source Thermal Ionization Mass Spectrometer (VG 354 TIMS) has been installed at Wadia Institute of Himalayan Geology. Akimasa Masuda Professor of Analytical Chemistry & Cosmochemistry in the Department of Chemistry donates this sophisticated instrument at the University of Electro-Communications, Tokyo, Japan. As part of Isotope Laboratory facility, clean-air chemical laboratory is being developed for sample processing and purification of reagents. With this modern facility being developed at WIHG, a wide range of earth & environmental problems and/or processes can be studied using radiogenic isotopes as tracers, in addition to training manpower.