Chapter EH
GEOLOGICAL SETTING C h ap ter II
GEOLOGICAL SETTING
Introduction :
The Dras-Kargil area, which has been studied during the course of the
present investigation, constitutes a part of the Ladakh Himalaya. It falls within the Indus-Tsangpo Suture Zone which for brevity is hereafter referred to as the
Indus Suture Zone. In this chapter the geology of Ladakh is briefly reviewed and the field characteristics of the varied lithological units occuring in the Dras-
Kargil area are detailed.
Tectonic Framework of Ladakh:
In the Kashmir region of northwestern Himalaya the NE-SW trending
Indus Suture Zone lies between the Ladakh Range and the Zanskar Mountains.
The tectonic framework and stratigraphy of this region has been described amongst others, by Thakur (1981), Honegger et al. (1982), Searle (1983). Three lithotectonic units, namely, the Zanskar Zone, the Indus Suture Zone and the
Ladakh Plutonic Complex are recognised from the southwest to northeast in the
Ladakh region. To the northeast of the Ladakh Plutonic Complex lies the Shyok
Suture Zone and the Karakorum Batholith. To the southwest of the Zanskar
Zone is the Central Crystalline Zone of the Higher Himalaya. The spatial
7 distribution of these tectonic zones is shown in the regional geological map
(Fig.2.1) which has been modified after Thakur (1981). The tectono-stratigraphy
of the Ladakh Himalaya, as reconstructed by Thakur (1981, op. cit.), is given in
Table 2.1. It is to be noted that in this table Thakur has shown the Ladakh
Plutonic Complex to be a part of the Indus Suture Zone; a position that is not
generally accepted.
In the Dras-Kargil area lithounits of the Zanskar Zone, the Indus Suture
Zone and the Ladakh Plutonic Complex are exposed. Hence a brief review of these three tectonic units is given below.
The Zanskar Zone :
The Zanskar Zone, which corresponds to the Higher Himalaya of Kashmir comprises of the Zanskar Crystalline Complex, the Zanskar Supergroup and the
Tso Morari Crystalline Complex.
The Zanskar Crystalline Complex consists of metasedimentary rocks, gneisses and migmatites, which show greenschist - granulite facies metamorphism and granites. The Rb-Sr ages of upto 1830 Ma suggest that they represent a reactivated crystalline basement (Thakur, 1981). The Zanskar
Supergroup (Nanda and Singh, 1977; Srikantia et al., 1978), having a thickness of over 9000m, consist of a fossiliferous sequence of Upper Proterozoic and
Paalaeozoic sediments with Permian volcanics and Mesozoic Eocene carbonates.
The Tso Morari Crystalline Complex includes metamorphosed Palaeozoic sediments of the Zanskar Supergroup.
8 Fig. 2.1 MAP SHOWING REGIONAL GEOLOGY OF LADAKH HIMALAYA. (modified after Thakur. 1981 ) The Indus Suture Zone :
This is a narrow belt of rocks averaging 20 kms in width and extending
over a distance of about 400 kms in Ladakh, that is quite distinct from the
crystalline units on either side. It comprises of flysch and molasse sediments,
plutonic-volcanic rock associations that are characteristic of a magmatic arc, and
ophiolite and ophiolitic melanges. The rocks of this belt were first studied by
Stoliczka (1866) and Lydekker (1883). Subsequently their main characteristics
were described by Dainelli (1934), Auden (1935), Wadia (1937) and Berthelsen
(1953). More recently a wealth of information has been made available through the publications of Mamgain and Itao (1965), Pande et al., (1969), Raiverman and Mishra (1974), Gansser (1974, 1977, 1979), Shah et al., (1976), Varadarajan et al., (1980), Thakur (1981), Honegger et al., (1982), Rai and Pande (1982,
1983), Searle (1983), Radhakrishna et al., (1984, 1987), Varadrajan and Vashist
(1986), Dessai et al., (1986), Anand (1989), Karmalkar et al., (1989), and
Varadarajan and Powar (1989).
The litho-stratigraphy of this belt has been recently described by Thakur
(1981) and Searle (1983). Their classifications are given in Table 2.2. The stratigraphy proposed by Thakur (1981) is followed here.
Lamayuru Formation : It comprises of shales, siltstones and graded sediments with flute casts which sometimes have intercalations of red radiolarian cherts. It has a thickness of about 1000 - 1500 m. Large blocks and lenticular bodies of limestones of Permian age, (Tewari and Pande, 1970), occur as exotic blocks
9 Tabic 2.1 : Stratigraphy of the Indus Suture Zone, Ladakh Himalaya.
Thakur(1981) Searle (1983) Age
Kargil Formation Indus Group
Conglomerates and Kargil Formation Neogene sandstones with occasional Fine grained sandstones, shales siltstones and shales
------T h ru st------Bazgo Formation : Red Cretaceous to Early sandstones and shales Eocene Indus Formation : Clastic Hemis Formation : Well sediments, conglomerates, bedded conglomerate sandstones, siltstones and shales with bands of Upshi Formation : limestone and dolerite sills Conglomerate
------Thrust------Thrust------
Shergol Melange: Shergol Ophiolitic Melange : Middle to Late Serpentinites, dunites, Serpentinised harzburgites Cretaceous peridotites within jasperoid and dunites, gabbros and shales, cherts, pillow lavas sheared volcanic rocks with and basic rocks deep sea sediments.
______T h ru st______------T h ru st------
Dras Formation : Andesitic Dras Volcanic Group Middle to Late and basaltic lavas with Tholeiitic to andesitic Cretaceous pillow structure, radiolarian volcanic and volcano-clastic chert, jasper and limestone sediments with limestone blocks ------T h ru st------Thrust------
Lamayuru Division : Lamayuru Complex : Shales, Triassic to Cretaceous Shales, siltstones and sandstones, turbidites with graded sandstones, blocks intercalations of radiolarian of limestone of Permian cherts. Exotic limestone age. occurs within the complex
Note: The Nidar Complex is the equivalent of Shergol Melange and not shown as a separate unit.
10 within the Lamayuru Formation and these have been designated as Mulbek
'exotic' limestones by Searle (1983). On the basis of reported Daonella sp.,
bivalves, crinoids and foraminifera recorded by various workers (Frank et al.,
1977; Shah and Sharma, 1978; Fuchs, 1977), the Lamayuru Formation is
assigned a Triassic to Cretaceous age.
Dras Formation : This consists of a thick ( over 3000 m) sequence of volcanic
rocks with associated volcano-clastic sediments. The volcanic rocks are mainly
andesitic and basaltic flows that show local association of pillow lavas and also
rare rhyolites. The volcano-clastic association includes agglomerates, radiolarian cherts, jaspers and limestones. The proportion of sedimentary rocks progressively increases from west to east, and in the eastern part shales and sandstones also occur. The limestones have yielded Orbitolina, Ilippurites and bryozoa which indicate a Middle to Late Cretaceous age.
Shergol Melange : This unit consists of bodies of serpentinite, peridotite, dunites and gabbros that occur in association with shales, cherts, pillow lavas and basic rocks. Microfauna of Middle to Late Cretaceous age has been reported from the sedimentary horizons by Shah and Sharma (1 977). Equivalent horizons in the eastern part have been designated as the Nidar Ophiolite and Zildat
Ophiolite Melange (Thakur and Virdi, 1979). Varadarajan and Vashist (1986) point out that the ultramafic-mafic rocks that are the most important constituent of the Shergol Melange, often occur as intrusive bodies within the Dras
Volcanics, and probably represent the last phase in the evolution of the Indus
Suture Zone.
11 Indus Formation : It consists of clastic sediments (conglomerate, sandstone,
siltstone and shale) having a stratigraphic thicknes of about 4000 m. The
sediments are intruded by sills of dolerite. This formation has been interpreted
by Pal et al. (1978) as being a flysch sequence of Cretaceous to Early Eocene age.
Kargil Formation : This formation which rests directly and transgressively on
the Ladakh Plutonic Complex, consists of conglomerates and sandstones with
occasional shale bands. It is a molasse sequence which has yielded fresh water
molluscs and Plant remains (Sahani and Bhatnagar, 1958), and also vertebrate
fossils (Dixit et al., 1971) indicative of Neogene age.
The Ladakh Plutonic Complex :
The Ladakh Plutonic Complex constitutes the 30 - 50 km wide Ladakh
Range to the north of the Indus Suture Zone. It largely consists of granites,
granodiorites, with which are associated pyroxenites, hornblendites, malic rich
gabbros, norites and anorthosites. According to Honegger et al., (1982) the
complex consists of 50% of rocks of granodioritic composition, 20 - 30% of intermediate rocks and 10 - 20% of mafic intrusives. The granodiorites are also
found to intrude the Dras Volcanics of the Indus Suture Zone. Pyroxene bearing pegmatites and hornblende bearing micro-dioritic sills intrude the Ladakh
Plutonic Complex. Radiometric dating of the Ladakh Plutonic Complex suggests a Late Cretaceous to Eocene age (Searle, 1983).
12 Geology of the Dras-Kargil Area:
Geological mapping carried out by the author shows the presence of a
variety of sedimentary and igneous rocks in the Dras-Kargil area. These include
limestones of the Zanskar Zone, litho-units of the Indus Suture Zone and igneous
rocks of the Ladakh Plutonic Complex. The spatial distribution of the important
litho-units is shown in the geological map (Fig. 2.2). The field characteristics of
the various rock types are described below.
Zanskar Zone : In the area mapped during the course of the present
investigations the Zanskar Zone is represented by the Matayin Limestone (Shah
et al., 1976). This unit consists of thick bedded limestones, often dolomitic that
contain intercalations of grey and brown shales. The limestones also include
occasional bands of coqina with crinoids and fragments of Rhynchonella sp.,
crinoids, Lima sp. and Pecten sp.. These limestones have been assigned a Triassic
age (Shah et al., op. cit.). The limestones are exposed between Pindras and
Matayin on the Srinagar - Leh road with the best outcrop being seen around
Matayin, about 9 km sout-west of Dras. The limestones dip at 15° to 50° toward
south. They are often strongly folded. The Matayin limestones have been thrust
over the Dras Volcanics along the south dipping Dras Thrust which is traced in
an east-west direction.
Indus Suture Zone :
The litho-units of the Indus Suture Zone, that are exposed in the area mapped, include the Dras Formation, the Shergol Melange, the Indus
13 0 0 l o i 75 50 76 00
F ig .2 2 : GEOLOGICAL MAP OF DRAS-KARGIL AREA , LADAKH HIMALAYA Formation and the Kargil Formation. This zone has been locally designated as
the Dras Volcanic Belt.
Dras Formation : It consists of a thick sequence of volcanic and volcano-clastic
rocks that constitute an east-west trending belt which extends from Pindras in
the west through Dras to Trizpan and beyond in the east. At Dras massive lava
flows are interbedded with limestones and tuffaceous zones (Plate 2.1, Photo 1).
The volcanics are generally fine grained, massive and greenish in colour. These
sometimes show a purple tinge. The basalts are generally of a darker colour here
and vesicular and amygdoloidal in character. In rare cases, pillow lavas are exposed. The andesitic flows are lighter in colour and include phenocrysts of pyroxene. Along the Dras Thrust the volcanic rocks are crushed and pulverised.
Thick flows of polymictic volcanic conglomerates are exposed to the south of the
Dras river, near Dras village.
At Pashkum aphyric, massive lavas are associated with thin red cherts, shales and sandstones. The basal flows show pillow lavas with the individual pillows being 0.5 m to 1.5 m in length and about 0.75 m in height (Plate 2.1,
Photo 2 and Plate 2.2, Photo 1). The upper part consists essentially of massive lavas similar in appearence to those of Dras. To the south of Pashkum the Dras
Volcanics are thrust over the Indus Formation (Plate 2.2, Photo 2) along the
Pashkum Thrust (Srikantia and Razdan, 1981) which also referred to as the
Kargil Thrust (Raiverman and Mishra, 1975), the Great Ladakh Thrust (Tewari,
1964) and the Great Counter Thrust (Berthelsen, 1953, Gansser,! 964). Near
14 Lotsum village the volcanic rocks near the thrust, exhibit a network of epidote
veins (Plate 2.3, Photo 1). In Manjigund-Trizpan section, Dras Volcanic rocks
come in contact with the Ladakh Plutonic Complex (Plate 2.3, Photo 2). In this
section, at places, the volcanic rocks show numerous silica veins (Plate 2.4,
Photo 1). Xenoliths of volcanic rocks are seen in granitoids of Ladakh Plutonic
Complex (Plate 2.4, Photo 2).
Shergol Melange: Mafic-ultramafic rocks, those are generally considered to be part of the Shergol Melange are exposed at three localities along an east-west trending belt within the Dras Volcanics. These occurrences are (i) a little to the north of Dras, (ii) at Thasgam and (iii) south of Pashkum.
At Dras, ultramafic rocks occur in the ‘Orange hill’ area in a lensoid outcrop extending over a length of 5 kms and having a maximum width of about
1.5 kms (Plate 2.5, Photo 1). On weathering these rocks yield orange coloured scree and soil cover which can be recognised from a distance. The ultramafic rocks consist mainly of peridotites and dunites. The peridotites which occur at the base of the section consist of sheared, mylonitised and serpentinised harzburgites. At higher elevation the harzburgite appears fresh and with decrease in ortho-pyroxene grades into dunite. However, dykelets and inclusions of harzburgite occur within the dunite. The harzburgites and dunites show chromite mineralisation with the chromite occuring in bands, lenses and pods, often imparting a banded appearence to the dunites. At places, pockets of magnesite are also seen. Associated with the ultramafic rocks are fine to coaise grained olivine gabbros.
15 At Thasgam, the peridotites, namely harzburgites, form the base of the
section and upwards grade into dunites. In the lower part of the section, the
harzburgite are highly serpentinised. These rocks are associated with gabbros
and pyroxenites. The gabbro is essentially a hornblende gabbro. At places it
becomes pegmatitic with the hornblende prisms attaining a length of upto 10
cms.
At Pashkum, the ultramafic rocks consist mainly of serpentinites (Plate
2.5, Photo 2). These occur in association with blocks of sandstones, cherts,
limestones and gabbros. In vicinity of the Pashkum Thrust the serpentinites
exhibit well developed slickensides (Plate 2.6, Photo 1).
Indus Formation : This unit, consisting of alternations of purple sandstones,
shales and conglomerates, is exposed around Pashkum in the eastern part of the
map area. It is separated from the Dras Volcanics and the Shergol Molango by the Pashkum Thrust. The shales and sandstones are generally green coloured.
The associated conglomerate contain pebbles of jasper, chert, lavas and granitoids.
Kargil Formation : The Kargil Formation is best exposed in the Suru Valley at
Baru, Akchamal and Kargil, and in the Wakha Rong river section. It consists of alternations of conglomerates, sandstones and occasional shale beds (Plate 2.6,
Photo 2). These beds dip 20° to 30° south-east (Plate 2.7, Photo 1). The Kargil
Formation unconformably overlies the rocks of the Ladakh Plutonic Complex
(Plate 2.7, Photo 2).
16 The Ladakh Plutonic Complex :
The Ladakh Plutonic Complex occurs in the northern part of the area
covered by the present investigations. It mainly consists of acid intrusives
including granodiorites and granites and also of mafic rocks mainly gabbros,
norites and hornblendites. Locally this igneous complex has also been
designated as the Kargil Igneous Complex (Rai and Pande,1978).
The granitic rocks vary from granites to granodiorites. Granodiorites make up the hill ranges (Plate 2.8, Photo 1) to the south of Kargil. The localities where they are well exposed include Manjigund and Titichung. There they show dominance of hornblende over other mafic minerals. In the north-western part the granodiorites are rich in biotite especially around Chainnigund and Kharbu.
In the Manjigund - Trizpan sector the granodiorites are seen to intrude the Dras
Volcanics. In the Manjigund-Titichung sector, the rocks are intruded by numerous dykes of dolerites (Plate 2.8, Photo 2). Northwest of Kargil, near
Chainnigund, the granodiorites contain xenoliths of gabbro and norites the size of which varies from few centimeters to 25 - 30 centimeters along the longer direction (Plate 2.9, Photo 1). The granodiorites are traversed by light coloured quartzo-felspathic veins (Plate 2.9, Photo 2). Near the Haraka Bahadhur Bridge, granodiorites, locally, display a weak gneissosity marked by parallel arrangement of biotite flakes.
Basic intrusives found in the Kargil area include norites, gabbros and hornblendites. Norites are exposed at Kargil, Poin and Akchamal. These are
17 dark green medium grained rocks which are often cut by aplitic veins (Plate
2.10, Photo 1). At Kargil the norite is exposed in the road section along the Suru
Valley, but is elsewhere covered by alluvium. A better exposure is seen at
Akchamal, east of Kargil, where norite outcrops over a distance of 1.5 kms. A third body is exposed at Poin, north-east of Kargil.
A gabbro body is exposed at the village Chainnigund. It is exposed over a distance of about 3 kms along the road section. At places, vertical gradation in grain size is well observed. Cumulus structure marked by plagioclase-pyroxene concentrations are seen at places (Plate 2.10, Photo 2). The crystals are upto one centimeter in size. Increase in the amount of hornblende and olivine locally gives rise to hornblende gabbro or olivine gabbro (gabbronorite) respectively. A homblendite is exposed in Manjigund - Titichung section covering an area of about one square kilometer. Tho rock shows tho development of schistosity due to parallel arrangement of hornblende needles and is cut by numerous quartz veins (plate 2.11, Photo 1) which trend in N25°E S25°W.
18 Plate - 2.1
Photo - 1 : Dras Volcanics interbedded with limestone at Dras.
Photo - 2 Pillow lavas in Dras Volcanics at Pashkum. Plate - 2.1
Photo 1
Photo 2 Plate - 2.2
Photo - 1 Pillow lavas in Dras Volcanics a t Pashkum.
Photo - 2 Dras Volcanics thrust over the Inaus Formation along the Pashkum Thrust at Pashkum. Plate - 2.2
Photo 2 Plate - 2.3
Photo - I Network of epidote veins in the Dras Volcanics in the Pashkum thrust zone at Lotsum village.
Photo - 2 Contact zone between Dras Volcanics (darker shade) in background and granitoids (lighter shade) of the Ladakh Plutonic Complex in foreground near Trispan village. Plate - 2.3
Photo 2 Plate - 2.4
Photo - 1 . Silica veins in Dras Volcanics in c o n ta c t with the Ladakh Plutonic Complex along the Manjigund-Trizpan section.
Photo - 2 : Inclusion of volcanic rock in granitoids of Ladakh Plutonic Complex at Manjigund. Plate - 2.4
Photo 1
Photo 2 Plate - 2.5
Photo - 1 : Ultramafic rocks of Shergol Melange exposeO at Orange Hill' area, Dras.
Photo - 2 : Serpentinites from the Shergol Melange at Pashkum. Plate - 2.5
Photo 1
Photo 2 Plate - 2.6
Photo - 1 Serpentinites exhibiting slickensides in the vicinity of Pashkum Thrust, at Lotsum.
Photo - 2 Interbedded conglomerates, sandstones and shales in Kargil Formation a t Baru. Plate - 2.6
Photo 1
Photo 2 Plate - 2.7
Photo - 1 : Southeast dipping Kargil Formation at Akchamal village
Photo - 2 : Unconformity between the Ladakh Plutonic Complex (lower) and the Kargil Formation at Titichung village. Plate - 2.7 Iff t
Photo 2 Plate - 2.8
Photo - 1 Hill ranges of granodiorite of Ladakh Plutonic Complex, south of Kargil.
Photo - 2 Dolerite dykes in granitic rocks of the Ladakh Plutonic Complex near Titichung in the Manjigund-Tifichung section. Plate 2 .8
Photo 2 Plate - 2.9
Photo - 1 Inclusion of basic rocks in granitic rocks of Ladakh Plutonic Complex, Chainnigund.
Photo - 2 Quartzo-felspathic veins in the granodiorites from Ladakh Plutonic Com plex, Silkche. Plate - 2.9
Photo 2 Plate - 2.10
Photo - 1 : Aplitic veins in norites at Akchamal.
Photo - 2 : Cumulus structure in gabbros of Ladakh Plutonic Complex at Chainnigund. Plate - 2.10
Photo 2 Plate - 2.11
Photo - 1 : Hornblendite with quartz veins exposed near Manjigund.
» Plate - 2.11
Photo 1