Geology of the Himalayan Belt. Deformation, Metamorphism, Stratigraphy

247 Pages·2016·14.434 MB·English

by  B.K. Chakrabarti

Geology of the Himalayan Belt
Deformation, Metamorphism, Stratigraphy
B.K. Chakrabarti
Director (retd.), Geological Survey of India

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Prof. Dhrubajyoti Mukhopadhyay
Foreword
“On the geological structure and relations of the of the southern portion of the Himalayan Range
between the rivers Ganges and Ravee” by H.B. Medlicott (Memoirs of the Geological Survey
of India, vol. 3, 1864) was the first attempt to provide a somewhat regional geological account
of a part of the Himalaya. “A Manual of geology of India, Part II: extra-peninsular area” by
H.B. Medlicott and W.T. Blandford followed it in 1879. Subsequently, detailed accounts of
several sectors of the Himalaya like Spiti, Kashmir, Shimla Hills, Krol Belt, Shali, and Darjeeling
appeared. However, a cogent panoramic continuity of various geological elements of the Himalaya
was lacking. This task was accomplished in 1964 by the famous book, “Geology of the Himalayas”
by Augusto Gansser. Although it laid the foundation of regional picture of the Himalaya, it was
a partial synthesis, as there was little geological information on Sikkim, Bhutan, and Arunachal
available at that time, and there were several gray areas pertaining to stratigraphy and structure
of the Lesser Himalaya. As an addition, some paradigmatic data poured in, and the need was felt
for updating this monumental work.
Towards the end of the 20th century, there were publications on the Western as well as the
Eastern Himalaya, but these did little to synthesize conflicting views. Geologists, particularly
younger ones, in different and isolated terrain, were like proverbial the four blind men feeling
the elephant. Their regional interpretations were locally biased, based on fractured observations.
Thus, there is an urgent need for a book that deals with the Himalaya as one entity and
provides a homogenous version of various aspects of geology of the Himalaya. I am happy that
Dr. B.K. Chakrabarti, who has been involved with the Himalaya since 1967, has undertaken
this marathon job of synthesizing the geology of all the geotectonic units from the north
to the south and from the east to the west. In a treatise like this, where several conflicting
interpretations and conceptual models exist in the literature, the synthesis by the author
is based on his concepts and experience, which at times can be biased. Everyone may not
agree with Dr. Chakrabarti’s views; there is no need also for a total acceptance. Descent
is essence for the progress of science, which is dynamic and vibrant. Unanimity on all the
aspects will spell an end to the progress of geology. What is important is the availability of
a book on the Himalaya incorporating all the latest data with a masterly review, which I am
sure Dr. Chakrabarti is eminently capable of.
O.N. Bhargava
xi
Acknowledgment
Interest in geology of the Himalaya was kindled in the late 1960s of the 20th century when I
joined an office of the Geological Survey of India, situated close to the Lesser Himalayan Belt.
Since then, although my assignments changed a few times, I could work on specially struc-
ture and metamorphism of the Lesser Himalayan Sequence. I did field study of a part of the
Himachal Himalaya and a little of the Eastern Himalaya. However, I was quite up-to-date with
the advancement in study of the entire Himalayan belt. I was looking after the Central Library of
the Geological Survey of India along with my other assignments, and every issue of the journals
contributed by the Survey reached my table before being catalogued. This helped me a lot not to
miss any article on Himalayan geology.
The Survey has a number of specialized divisions, and I had the opportunity to interact with the
specialists of these divisions and get their help to generate data on my topics of work. I owe a
great deal to my colleagues for enriching me in my studies. It has been a tough job at 73 to write
a manuscript on the Himalaya with very restricted facilities available at home. I am indebted
to Prof. Bapi Goswami of the Department of Geology, University of Calcutta, for mailing me
articles I desired to go through. I thank my well-wishers for encouragement. Thanks are due to
my wife, Sabita, and son, Sumon, for cooperation.
B.K. Chakrabarti
xiii
About the Book
This publication covers discussion on deformation, metamorphism, and stratigraphy of the
Himalayan belt. The first nine chapters deal with a brief description of the geology of the belt
and its different sectors from Pakistan Himalaya in the west to Arunachal Himalaya in the
east. Chapter “Review of previous work” describes the observations of different workers on the
topics of this publication and attempts to review these contributions. Chapter “Deformation,
metamorphism, and tectonostratigraphy” covers a detailed discussion on high- and ultra-high
pressure metamorphism, on Tertiary metamorphism (especially the HT-LP phase), on the
evidence of Precambrian metamorphism, and on tectonostratigraphy, especially of the Precambrian
terrain of the Lesser Himalaya.
xv
1
Chapter

Lithotectonic Subdivisions of the
Himalaya
1.1 L ITHOTECTONIC SUBDIVISIONS
The Himalayan belt has been subdivided into a few commonly accepted
longitudinal zones bounded by major thrusts or faults. From south to north,
these zones and megatectonic features, such as fault and thrust, are the Main
Frontal Thrust (MFT), the Sub-Himalaya between the MFT and the Main
Boundary Thrust (MBT), the Lesser Himalaya between the MBT and the
Main Central Thrust (MCT), the Higher Himalaya between the MCT and
the South Tibetan Detachment System (STDS), the Tethyan Himalaya, and
the Indus-Tsangpo Suture Zone (Gansser, 1981) (Fig. 1.1).
Dipietro and Pogue (2004), however, maintain that such a subdivision of
the Himalayan belt is valid for India and Nepal sectors. The Pakistan sector
has difficulties in maintaining such a division across the syntaxial region
and extension of the MCT and the Higher Himalayan Crystallines (HHC)
across the Hazara Syntaxis to Western Pakistan is problematic (Fig. 1.1).
They refer in support to Hodges (2000), who opined that it is impossible to
correlate the metamorphic core of the orogen west of the Nanga Parbat Syn-
taxis with the Greater Himalayan zone of the Central Himalaya. Gansser
(1964) did not extend the MCT across the syntaxial region, although he
considered the metamorphics of the Pakistan sector as Central Crystallines
(HHC).
Heim and Gansser (1939) recognized the presence of a thrust in Central
Himalaya (the original MCT) at the base of the gneissic rocks of the HHC.
Valdiya (1980), however, considers this original MCT of Heim and Gansser
(1939) as the Munsiari Thrust; the MCT (his Vaikrita Thrust) lies higher up.
In the Garhwal–Kumaon sector of Central Himalaya, the Munsiari Thrust
(original MCT) and the higher level Vaikrita Thrust of Valdiya (1980) divide
the original HHC zone into a lower MCT zone (the Munsiari Group) and a
higher level Vaikrita Group. Arita (1983) designated the Munsiari and the
Vaikrita Thrusts of Valdiya (1980) as MCT and MCT , respectively, in
1 2
Geology of the Himalayan Belt. http://dx.doi.org/10.1016/B978-0-12-802021-0.00001-2
1
Copyright © 2016 Elsevier Inc. All rights reserved.
2 CHAPTER 1 Lithotectonic Subdivisions of the Himalaya
THBV
HHC
MBMTFT MCT TS THSHCbZaasninskarspitiTSNb.Kasuimnaon TS TS STDS ITSZ
SR LHS Wba.sNinepalTS TS TS TS HHC +
HHC
MCT
LHS
SD
GD MS
Delhi GBF FR
Aravalli- B INDEX
TS Tethyan Sequence (TS)
Siwalik/Tertiary granite
Deccan Traps
Gondwana
N 300 Km
Vindhyan
LHS/HHC
+ Granite-gneiss bodies
Proterozoic mobile belt
Cratonic domains
n FIGURE 1.1 Lithotectonic zones in the Himalaya and the adjacent peninsula. MFT, Main Frontal Thrust; MBT, Main Boundary Thrust; MCT, Main Central
Thrust; STDS, South Tibetan Detachment System; ITSZ, Indus-Tsangpo Suture Zone; LHS, Lesser Himalayan Sedimentaries; HHC, Higher Himalayan Crystallines
(with granitoid bodies); THBV, Trans-Himalayan Batholiths and Volcanics; GD and SD, Gandak and Sarda Depressions; SR, FR, MS, Sargodha, Faizabad, and
Monghyr-Saharsa ridges; B, Bundelkhand granite; GBF, Great Boundary Fault. Source: Chakrabarti, 2009. (copyright permission for reproduction from
Capital Publishing Company, New Delhi.)
central Nepal (Fig. 1.2). The HHC sequence overlying MCT is named the
2
Himalayan Gneiss zone by Arita (1983).
Thakur (1977) observed the phenomenon of divergent isograds in the
HHC. He, however, supported the position of the MCT as that of Heim and
Gansser (1939) (Fig. 1.2). While the lesser Himalayan sequence so com-
monly displays a reversed order of metamorphic grades, Thakur (1977)
observed both normal and reversed metamorphic grades in the HHC (his
divergent isograd picture). Thakur reported a general decrease in meta-
morphic intensity on either side of a core of high grade metamorphism in
the HHC zone of the Himachal Pradesh covering areas like Kullu, Manali,
Rohtang, and Khoksar to the border of the Tethyan sequence (Baralacha).
V Valdiya’s Main Central Thrust V T
M (Vaikrita Thrust) V
LHS MLHMSUNSIARI[M] VAIKRITA (V) V Tethyan Sequence T V V V
M LHS M MCT2 V M MCT ZONE
M M L H S
M MCT1
LHS
100 Km ALMORA
LHS Kathmandu
MT
n FIGURE 1.2 The Vaikrita and the Munsiari Thrusts. M, Munsiari Group and the Lesser Himalayan Crystallines; MT, Munsiari Thrust; V, Vaikrita Group; LHS, Lesser Himalayan Sedimentaries; MCT,
1
Main Central Thrust of Arita (1983); MCT, Vaikrita Thrust/Main Central Thrust (Arita, 1983); X and T, Tertiary granite. Source: Chakrabarti, 2009 (copyright permission for reproduction from Capital Publish-
2
ing Company, New Delhi.) 1
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