Geology of India (Volume 1)
By M. Ramakrishnan and R. Vaidyanadhan
Published by the Geological Society of India,
PB. 1922, Gavipuram P.O., Bangalore - 560 019
Pages: xxxii +556
Himalaya is among the youngest mountains of the world
that is still growing. It is a product of India-Asia plate tectonic collision, and is
a classical example of continent-continent collision in the world.
Traditionally, the Himalaya is divided geologically into six zones, 6th zone: The Trans-Himalayan batholiths (Karakorum, Ladakh and Kailas-
Mansrovar) forming a large linear plutonic complex of I-type plutons
(gabbro-diorite-granite) ranging in age from 110 to 40 Ma occurs to the
north of the Indus-Tsangpo and Shyok suture zones.
Tso Morari Crystallines (TMC) of Ladakh (Kashmir) belong to the Trans-
Himalayan Zone and are exposed in an elongate NW-plunging dome with a
100 km long axis. T M C consists of quartzo-felspathic gneisses and
metasediments, along with Palaeozoic intrusive granitoids. Three phases of
deformation are recorded in TMC, viz., early NW-SE trending isoclinal folds,
followed by coaxial open to tight folds, and the later NE-SW trending open
folds. Garnetiferous quartzofelspathic gneisses with lenses of eclogite are
included in the Puga Formation (Palaeoproterozoic) that is correlated with the
Central Crystallines. About 25 eclogite lenses and sills are mapped within the
TMC and represent ultrahigh pressure (UHP) metamorphism along the leading edge of the Indian plate at a depth of -100 km around 55 Ma. Younger granites
(-460 Ma) intrude the Tso-Morari dome.
Suru-Giambal (Zanskar) and Rohtang Crystallines of Himachal
Pradesh belong to Vaikrita Group. They are exposed in two important and
independent antiforms of the basement complex. The Suru-Giambal gneiss
extends for 200 km from Lahaul in Himachal Pradesh to Sanko in Ladakh, and
consists of two units. The lower unit is made of banded quartzofelspathic gneiss
and garnet-staurolite-kyanite-sillimanite gneiss having interbands of
amphibolite and cordierite-anthophyllite gneiss. The upper unit consists of
quartz-biotite-muscovite schist, amphibolite, quartz-muscovite schist, calc-
phyllite and marble. Migmatitic gneiss consists of melanocratic palaeosome of
garnet-staurolite-mica schist and neosome of leucocratic quartz-felspar gneiss.
Pegmatites and aplites containing tourmaline intrude the mica schists. Wangtu
gneiss of Vaikrita Group has Rb-Sr age of 2025±86 Ma. Rohtang gneiss consists
of a series of layered psmammitic gneisses and mica schists of great thickness
exposed for 250 km between the Chanderbhaga and Sutlej river valleys, in a
NW plunging antiform. Unlike in other parts of Central Crystallines where
metamorphic inversion is noticeable, here the metamorphism is reported to be
progressive in the normal order from chlorite to sillimanite grade (Srikantia
and Bhargava, 1998, p. 192). The temperature range of progressive metamorphic
zones is 540°, 560°, 640° and 650°C. Extensive intrusions of granite to
granodiorite (Rakcham, Karcham, Mantalai, Manikaran and Gangotri
granitoids) of Pan African age (-580 Ma) abound in the Rohtang gneiss.
Leucogranites of 14-28 Ma age are also reported.
The Indus-Tsangpo Suture Zone or the Main Mantle Thrust shows _F1
folds that are tight to isoclinal with axes trending NW-SE to WNW-ESE and
having moderate plunge on either side. Cross folds and thrusts are seen locally.
The Shyok Suture Zone and the Main Karakoram Thrust are considered older
than the Indus Suture Zone. The collision of India with Asia was considered
diachronous, resulting in oblique convergence beginning in western Himalaya
at 65-55 Ma and terminating in the east at 50-45 Ma, with the counterclockwise
rotation of India (Fig.4H-3).
The Trans-Himalayan zone consists of calc alkaline volcanics, Kohistan and Ladakh batholiths (including numerous gneiss domes), Chilas igneous
complex, Gandise magmatic belt of Tibet and Indus Formation in the western
sector. The Indus Formation is interpreted either as Cretaceous arc-trench gap
sediments or Tertiary continental deposits overlying the batholith. Similarly,
in the eastern sector, the Lohit granodiorite and Tidding Formation are separated
from the Tethyan Himalaya by the Tidding Suture of post-Lower Eocene and
pre-Middle Miocene age. In the northwest, the Karakoram batholith associated
with Pangong Tso Formation is separated from the Tethyan Himalayan belt by
the Shyok Suture Zone that is reworked along the Main Karakorum Thrust.
The Pangong Tso Formation is involved in three phases of deformation, with
isoclinal _F1 folds, open folds of F 2 coaxial with F 1 and open F 3 folds associated
with parallel faults.