Chapter n INTRODUCTION C h ap ter I
INTRODUCTION
Prologue :
The Himalaya has, for over a century, attracted the attention of geologists from all over the world. Painstaking investigations carried out by them have established the geological framework of this lofty mountain chain. Amongst the various lithotectonic units that have been identified the Indus-Tsangpo Suture
Zone is perhaps the most enigmatic. It has been traced for about 2,500 kms along the entire length of the Himalaya; for the greater part following the courses of the Indus and Brahmaputra (Tsangpo) rivers (Gansser, 1964). This
‘suture’ is generally considered to be the boundary between the Indian and
Eurasian plates (Le Fort, 1975; Molnar and Tapponier, 1975; Gansser, 1975). It corresponds to a Cretaceous subduction zone along which there has also been the obduction of oceanic crust onto the continent (Dewey and Bird, 1970; Powell and
Conaghan, 1973; Gansser, 1977; Bally et al., 1980; Thakur, 1981 and
Shackleton, 1981). The segment of this suture zone that has been best studied is the Dras Opholitic Belt of the Ladakh region of Kashmir where Tethyan sediments are associated with ophiolites and ophiolitic melange and with varied plutonic and volcanic rocks. A comprehensive project for the study of this belt has been undertaken by the Department of Geology, University of Poona and the present study forms a part of this project. The main objectives of the present
1 study were to:
i. identify and map the various lithological units constituting the Dras
Ophiolite Belt in the Dras-Kargil area,
ii. undertake petrographical and chemical studies of the magmatic rocks
occuring in this sector, and
iii. establish on the basis of above studies, the genesis of important rock
types occurring in the area and also the petrogenetic relationships
between the different rock groups.
Area of Investigation :
As indicated above, during the course of present study the Dras-Kargil
sector of Dras Ophiolite Belt has been studied. The area which is bounded by \ 0 latitudes 34° 25' 10" N and 34° 37' 00" N, and longitudes 75° 10’ 00" E to 76° 42'
00" E is included within 1 : 50,000 topographic sheets 43 N /ll, 43 N/15 and 52
B/2 and 52 B/6 of the Survey of India. Administratively this area forms a part of
the Kargil district of Jammu and Kashmir. The town of Kargil is a strategic military station, which lies 205 kms northeast of Srinagar, and can be reached by a fair-weather road connecting Srinagar to Leh. Dras is a small hamlet on this road located about 140 kms from Srinagar. The Srinagar-Leh road remains open only during June to September and fieldwork has to be confined to this period. Other important localities which are accessible only by a fair-weather road are Thasgam, Pashkum, Ackhamal, Chainnigund and Manjigund. The locations of these places are shown in the Location map (Fig. 1.1).
2 GILGIT I
B TOWN A ^ RIVER 0 80 ROAD km ^ INTERNATKINTERNATIONAL BOUNDARY
AREA UNDER STUDY
g 1.1 LOCATION MAP OF DRAS KARGIL AREA, LADAKH HIMALAYA. Topography :
Physiographically the Dras-Kargil area forms a part of the Ladakh
Himalaya. It presents a rugged topography with elevation ranging from 2,800 m to more than 5,000 m. The highest point in the area is the Somau peak (5,168 m) near Kargil. The area is dissected by several perennial streams forming a part of the Indus river system. These include the Suru river, the Wakha Rong river, the Dras river and the Shingo river and their tributaries. The Dras river flows from west to east and meets the Shingo river near Chainnigund. The latter meets the Suru river, a tributary of Indus river, near Silkcha (north of
Kargil). The Wakha Rong river flows from the southeast of Kargil and meets the
Suru river, NNE of Kargil. All these rivers flow along deep, steep-sided, rocky gorges that have only thin alluvium deposits on their floor. The drainage pattern is largely dendritic. These rivers are a fine example of an antecedent drainage.
Climate :
The climate is cold and there is considerable snowfall in winter i.e. between the months of October and February. The area remains snowbound upto April or May. The short summer extends from May to August or September during which the climate is pleasant. During summer the maximum temperature at mid-day is about 30° C while the night temperature may fall to below freezing point. During winter, the temperature is invariably sub-zero (sometimes even below -50° C). Dras is in fact, the second coldest inhabited place in the world.During the winter the region is totally cut oil from the rest of the country.
3 Previous Work :
The earliest publications on the geology of Ladakh were those by
Thompson (1852), Stoliczka (1866), Drew (1875) and Lydekker (1880,1883),
Oldham (1883), McMohan (1901), Hayden (1907) and Middlemiss (1911).
Subsequently Dainelli (1934) described findings of an Italian expedition to the
Ladakh Himalaya. A little later, Heim and Gansser (1939) undertook traverses
from Maglang pass to Kailas, and from Balchadhura to Upper Sutlej.The concept
of an Indus-Tsangpo ‘Suture’ was developed by Gansser (1901, 1974a,b, 1977),
according to which the suture represents a zone of collision between the Indian
and the Eurasian plates. The geological setting and stratigraphy of the Indus
Suture Zone has been largely studied by the geologists of Geological Survey of
India and Wadia Institute of Himalayan Geology ( Gupta and Kumar, 1975;
Tewari, 1964; Shanker et al., 1976; Frank et al., 1977; Virdi et al., 1977;
Srikantia and Bhargava, 1978, and Srikantia and Itazdan, 1980). The structural evolution and tectonics of the Indus Suture Zone has been evaluated by Windley
(1983), Searle (1983, 1986) and Thakur and Misra (1984). The ages of the granitic rocks from the Indus Suture Zone have been determined by different workers including Saxena and Miller (1972), Brookfield and Reynolds (1981),
Honegger et al., (1982), Sharma and Choubey (1983) and Schaerer et.cil., (1984).
The Dras-Kargil sector, which is the subject of the present study, has been studied from the point of view of stratigraphy, petrography and geochemistry by a number of workers. De Terra (1935) recognised flysch deposits
around Kargil and also reported the occurrence of volcanic rocks in this area.
4 Auden (1935) described these volcanic rocks. However, the first comprehensive
studies were undertaken by Wadia (1937). lie studied the volcanic rocks and
pyroclastic sediments and named them as the Dras Volcanics. Subsequently,
stratigraphical studies were undertaken by Norin (1946) and Berthelsen (1953).
Sahani and Bhatnagar (1958) reported plant fosssils in the Kargil Formation.
Manigain and Rao(1965) studied the Dras Volcanics in relation to the associated
sedimentary rocks. Shah et. al., (1976) described the stratigraphy of this sector.
Geochemical studies of the Dras Volcanics were carried out recently by
Gergan(1978), Shah and Gergan (1978), Rai and Pande(1982), Honegger et al.,
(1982), Gupta et al., (1983), Radhakrishna et al., (1984) and Raiverman and
Gopalaswamy (1989). The granitic rocks of the Kargil area form a part of the
Ladakh Plutonic Complex (Gansser, 1979) and have been studied by
Varadarajan et al. (1980), Rai (1980, 1982) and Honegger et al. (1982). The basic intrusives of the Kargil area have been studied by Rai (1977, 1979), Rai and
Pande (1983) and Dessai et al. (1986). Ultramafic rocks and associated chromites of this area have been studied by Prasad et al. (1976, 1980), Varadarajan and
Jhingran (1977), Prasad and Singh (1981), Prasad (1985), Varadarajan (1985),
Varadarajan and Vashist (1986), Karmalkar (1987), Radhakrishna et al. (1987),
Anand(1989), Karmalkar et a l (1989) and Varadarajan and Powar (1989).
Radiometric ages have been determined for the rocks of this region by different workers including Sharma et al. (1978), Brookfield and Reynolds (1981),
Honegger et al. (1982). Dating of the rocks has also been carried out by fission track techniques (Agarwal and Sharma, (1986). More detailed references to the above cited works are made at relevant places in the main text.
5 Method of Study :
The present investigations included field studies and laboratory
investigations which were carried out during 1984 to 1989. The procedures
adopted are outlined below. Field studies were undertaken during three different
visits, of about a month each, to the area during the field seasons of 1983, 1985
and 1987. The topography being rugged, the observations were largely restricted
to outcrops along the roads, foot-paths and mule tracks. About 250
representative rock samples were collected. Interesting geological features were
studied, sketched and photographed. A geological map on a scale of 1:50,000 was
prepared on the basis of the above observations. Two hundred thin sections of
representative rock samples were studied under the microscope. Modal analyses of 38 rock samples were carried out on a point counter following the Rosiwal method. Optical properties of minerals, and An - contents of plagioclase were determined on a four axes universal stage. About 52 samples were analysed for their major element content following the rapid analysis method of Shapiro and
Brannock (1962). Duplicate analyses for 25 samples were carried out by X-ray fluorescence at the Indian Institute of Technology, Bombay. Trace elements of rock samples were determined by atomic absorption spectroscopy at the Shivaji
University, Kolhapur. Rare earth element analyses of 21 samples were provided by the Central Chemical Laboratory of the Geological Survey of India, Calcutta.
Electron microprobe analyses of 68 minerals were carried out by Dr. Anand
Mohan at the University of Kiel, Federal Republic of Germany.
6