Annual Report 2000-2001

Scientific Research

Deep Continental Studies (DCS)

Deep Continental Studies (DCS) Programme is a collaborative, multi-disciplinary Earth Science Research Programme aimed to develop understanding of the deep crustal configuration and related processes of the Indian Lithosphere. During the year of report, efforts have been made for integrated geological and geophysical studies along selected transects or study areas.

New Projects

The following new projects have been sanctioned during the year 2000 :

• Development and dissemination of contours to images methodology for geoscientific data to aid deep continental studies in India.(AEG, Hyderabad)
  
• Study of the structure of the ophiolites of the Indus Suture Zone by using gravity and magnetic data along HIMPROBE Geotransect. (UOR, Roorkee)
  
• Modelling of fluid migration and behaviour in subduction related metamorphism in Indus Suture Zone (ISZ) Ladakh (WIHG,Dehradun)
  
• Metallogenic evolution of gold and copper mineralisation in the Sakoli Group.(ISM,Dhanbad)
  
• Evolution of ore fluids and gold metallogeny: a case study from the gold prospects in Eastern Mahakoshal Greenstone belt along Son- Narmada Lineament.(ISM, Dhanbad)
  
• Deep continental and tectonic studies of Chhatisgarh by gravity- magnetic methods. (BHU, Varanasi)
  
• Development of global optimization strategies to interpret gravity anomaly.(ISM, Dhanbad)
  
• Sm-Nd and Rb-Sr geochronological constraints on the Precambrian Southern Granulite Terrain, Southern India.(NGRI, Hyderabad)
  
• Gravity, Magnetic measurement along Siliguri- Gangtok-Lachung profile in Sikkim Himalaya.(NGRI, Hyderabad)
  
• National Facility on Geochronology/Isotope Geology( UOR, Roorkee).

Ongoing activities

Setting up of a national facility on Geochronology/ Isotope Geology University of Roorkee, Roorkee.

Initiative has already been taken regarding renovation of the laboratory, tendering for the equipment etc. A Project Implementation and Monitoring Committee has been constituted to look after the facility.

Geophysical study of the Indian sub-continent and its contiguous region for understanding the complexities of deep crust.

Under the above mentioned project, An aeromagnetic map was prepared by IIG, which clearly demarcates a NW-SE linear trend passing through the western margin of the Cuddapah basin up to Chennai which pass through known kimberlite pipe occurrences at Wajrakarur. It also maps the charnockites, intrusives and iron ore bodies of South India. Based on seismic sections, gravity data and available drill hole data, the position of Vedic Saraswati river has been demarcated.

HIMPROBE (NW Himalayan Geotransect)

Magnetotelluric studies carried out along parts of the geotransect viz. Mandi-Una region and Ladakh region have provided some significant results. The region between Himalayan Foot Hill Thrust (FHT) and Main Boundary Thrust (MBT) has been subjected to compressional forces resulting from the intercontinental collision and thus hosts a number of thrusts, synclines and anticlines, which are clearly brought out in the geoelectric structure. A conductive layer is delineated below the stations SW of station 9, which seems to rise in to the crust to depths of about 30 km below the Lambagraon syncline, presumably due to the fluid release from the deeper strata. This seems to be the western shoulder of the Simla-Almora ridge, observed in the gravity studies.

The geoelectric structure across Indus Tsangpo Suture Zone (ITS) and Shyok Suture Zone( SSZ)) shows three high resistivity bodies at shallow depths. First resistive layer on the south corresponds to the exposure of the Tso-Morari Crystalline complexes and extends to depths of about 15 km. The second resistive body corresponds to the Ladakh Batholith and is separated from the Tso-Morari Crystalline complexes by the Indus Tsangpo suture. Further NE, the third resistive body is located in the region of the Chushul Batholith separated from the Ladakh Batholith by Shyok suture. Both sutures were associated with high conductivity of 20-50 ohm-m. The Indus Tsangpo Suture was mapped as a NE down-dipping conductive zone with resistivity of 20-50 ohm-m up to depth of 25 km. Further NE, it becomes sub-horizontal below the Ladakh and Chushul Batholiths. The deeper signatures of the Shyok Suture were not obvious from the MT studies.

The geochemical and geochronological works of the Tso-Morari Crystaline along the HIMPROBE geotransects are in progress.

Development of parallel Seismic data processing Algorithms

A new Acoustic wave modelling algorithm has been developed in PARAM 10000 which considerably reduces the computer time using larger time steps.. This algorithm has been tested with oil exploration data set of ONGC. An attempt is being made to write codes in such a fashion that the computations and communications overlap to a great extent.

• Integrated Geotransect (Kuppam-Palani) across the Southern Indian Shield

Integrated geophysical/ geological studies viz. Seismic reflection, refraction/ wide angle reflection, gravity, magnetic, magnetotellurics were used along Kuppam-Palani transect to evaluate the crustal configuration and tectonic evolution of the southern granulite terrain. The seismic refraction/ wide angle reflection studies indicate a 5 layer surface configuration for the southern granulite terrain and an average crustal thickness of 45 km.

Completed projects

• Geophysical interpretation along Nagaur-Jhalwar and Jaipur-Raipur geotransects for scaling geology.

The total intensity magnetic profile and gravity profile along the Nagaur-Jhalwar transect and gravity profile along Jaipur- Raipur transect have been interpreted using fractals approach. The mid-crustal domal structure below the Delhi fold and Bhilwara Super Group was observed, which agrees with the results of seismic reflection studies. The depth of the Moho below the Vindhyan basin has been interpreted as 34 Km. The two step approach for dealing with non stationary gravity profile yielded the finer description of the subsurface along the transect.

• The magnetotelluric studies in the Jadcherla- Raichur-Dharwar-Goa Profile

The above mentioned study has delineated a thicker crust on the west of the Chitradurga Boundary fault. On the east, the crust was thin (12km) with a crustal downwelling below the MT station. The upper crust was about 18 km thick below Kushtagi. A Vertical Lower crustal conductor was observed below Chitradurga boundary fault extending to depths of 35 km from the bottom of upper crust.

• Gravity, magnetic and electrical resitivity studies along Jedcherla-Raichur-Panaji transect.

The above mentioned study indicates that the Moho below the Dharwar Schist Belt is found to be at a depth of 40 km unlike the average of 37 km below the transect. The sag is due to a depression in Moho boundary along various faults and is found to be occurring in between 100 to 200 Km from the west coast. The eastern boundary of this sag lies approximately below Gadag-Chitradurga Schist Belt. The shear zone with an extent of 400 Km length and 1-2 Km wide along the eastern boundary of the Gadag-Chitradurga Schiest Belt represents the boundary of the two Dharwar blocks. Velocity analyses based on DSS also corroborates that the boundary lies in the same region.

New Initiatives

• With a view to give a refreshed knoweldge about the mantle plume a two days workshop on "Plume Tectonics" was held on 13-14 , June 2000 at National Geophysical Research Institute, Hyderabad. Nearly 50 participants including lecturer, scientists and research scholars from all over India participated in the workshop. A series of themes covering the topics of mantle plume and granulite formation, Neoproterozoic bimodal volcanism, plume and lithospheric interaction, mantle plume and metallogeny, Deccan related plume activity, geothermal regime and geodynamic implication, plume activity in the Precambrian of India , plume activities and biological events were covered in the workshop. A set of recommendations has been finalized which will help in concretization of a few projects.
  
• The Indo-Gangetic basin has formed during the Cenozoic era in the northern part of the Indian Shield as a fore deep of the Himalayan orogenic system.. Very little information on the nature of sediments or the structure of the basin is available now. Considering the imoprtance of the study, a new programme is being initiated by DST for which a status report has already been prepared.

Publications

• With a view to disseminate information regarding achievements of the Projects under implementation and other issues related to the DCS Programme, DCS Newsletter is being brought out. 2 issues of the DCS Newsletter have been brought out during the current year.
  
• A section on Deep Continental Studies Programme has been brought out by IGC, Roorkee as a part of Research Highlights in Earth System Science. This volume primarily incorporates highlights of the work carried out under different DCS projects funded during the recent years.

National Programme on Global Positioning System

Department of Science and Technology has evolved a National Programme of GPS and other geodetic studies for monitoring the crustal deformation due to earthquake occurrence and other geodynamic phenomena on the recommendations of an Expert Group set up for the purpose. The Group recommended that an extensive GPS control network consisting of permanent stations, semi-permanent stations and field stations should be established. Further it has been recommended that a consortium approach, involving all the organisations that are active in this field, should be adopted. A project related to GPS studies for crustal deformations in Maharastra has already been funded to IIT, Mumbai. Setting up of 21 permanent GPS stations has been recommended by the PAMC-DCS/Expert Group which are in various stages of implementation.

Permanent stations at Dehradun, Dharmasala, Hanle, Almora and Kodaikanal have already been established. The establishment of other permanent GPS stations by institutions like WIHG, GSI, ISM ,GND University and SOI is under progress.

On-going projects

• In a project entitled "Earthquake Monitoring in Peninsular India by Geodetidc Methods using GPS by Survey of India, Dehradun". It was informed that SOI has established precise order network of 175 stations. As on date dense local network of 85 stations have been established. GPS observations on 80 stations are proposed to be completed during the current year.
  
• Crustal deformation studies in NW Himalayan region using GPS aided geodetic technique is being carried out by WIHG, Dehradun. Under this project, two Permanent GPS stations were installed in October, 1998, at DehraDun and Dharamsala (HP). More than 50 campaign-mode GPS stations were installed in the Lesser- and Higher Himalayan regions of north-western Himalaya, covering the entire states of Himachal Pradesh, and Uttaranchal. Repeated measurements of these GPS stations collected since 1996, in combination with data from permanent GPS stations located at Nepal (NAGA), Bangalore(IISC),Lhasa(LHAS), and other Central Asian sites(KIT3, POL2) were processed using the GAMIT software. Velocity vectors (in mm/yr) relative to Bangalore, for a few selected stations are shown in Fig.1. Analysis of the results obtained from the GPS sites distributed over the NW Himalaya show that crustal shortenning is taking place at nearly 15-20mm/yr rate, confined within a narrow zone of 100-150km north of the Himalayan Frontal Fault. Model inversion of the GPS data shows that nearly 50km length of the frontal thrust system is locked with the advancing India plate along the detachment surface, at depths of 6-10km. The accumulated strain will be released through future great earthquakes, whose epicenters are more likely to be located along the southern border of the Higher Himalayan range, where northern front-head of the locked detachment surface lies. Lateral segmentation exists along the Himalayan frontal thrust system. The Nahan Salient, lying in-between the Kangra and Dehra Dun re-entrants slides down the detachment surface more smoothly, thus having less earthquake potential compared to the adjacent Kangra and Dehra Dun regions.