Bulletin of the Oil and Natural Gas Corporation Limited
V.30, No.2 (December 1993), p.19-25, 2 figs.
India and China Forming a Single Plate – Evidences from Himalaya, Arabian Sea and China .
The Himalayan fold mountain belt is supposed to have risen from the Tethys Sea owing to the northward movement of the Indian shield and its underthrusting below the Eurasian Plate along the Indus Tsangpo Suture Zone. The author proposes a totally new concept of Himalayan Basin which was divided into two - separated by Delhi - Hardwar - Harsil Ridge (DHH). The DHH Ridge forms a boundary -a tectonic one, from Chagos in Indian Ocean to Okhotsk Coast in Russia via Lakshdweep, Cambay, Aravalli Range, Altyn Tagh, Nanshan, Ordos and Khingan Mountain. The geological sequences to the east and west of the DHH are quite different right from Early Paleozoic to Middle Tertiary. Even the older Vindhyans are restricted by the DHH. The Lesser Himalaya represents typical Vindhyans.
This concept has been supported by geomorphic features like drainage, hill ranges, deserts, plateau and also by geophysical aspects like thickness and conductivity of the crust besides geology including the Gondwanas. The frequent occurrences of earthquakes, Tertiary volcanism and related hazards are mainly along this boundary (DHH).
This theory encompasses mainland of India, Central and Eastern Himalayas, Tibetan plateau, Mainland of China, eastern Siberia (Russia) and Mongolia within one single plate/continent.
The Himalayan mountain chain is supposed to have been formed due to the collision of Indo-Australian Plate and Chinese (Eurasian) Plate (Gansser, 1946; Molnar, 1986 and Qureshy, 1971). Both the plates are continental and subduction has taken place along the Indus Suture Zone on the northern boundary of the Himalayan range (Thakur and Sharma, 1983; Thakur, 1992; Valdiya, 1980 and Sinha, 1989). The Indo-Australian Plate is considered to be moving in NNE direction at the rate of 3-5 cm per year and as a result of this collision, the youngest fold belt in the form of Himalaya has risen out of the Tethys Sea. Kaila and Hari Narain (1976) have placed the plate boundary north of Tibet and then through KunLun to Kirthar which finally merge with Owen Fracture in the Arabian Sea as shown in their first figure. Raiverman (1986) has dealt with the controlling factors during the Cenozoic period.
The author has a new concept regarding the northern boundary of Indo-Australian plate with the following observations :
The Himalaya does not make the plate boundary; instead India, Tibet and China form one plate.
A major fundamental fracture partly represented by Delhi - Hardwar -Harsil Ridge exists on its western limit [Chagos - Lakshdweep submarine ridge, Aravalli ranges, DHH underground ridge, Astin Tagh (Altyn Tagh) Qilian mountain, Ardos, Khingan mountain]. The Delhi - Hardwar - Harsil underground ridge divides the Himalaya Into two parts - eastern and western.
The eastern part comprises Nepal, Kumaun and eastern Garhwal and is designated as segment I, while the western part consists of Himachal, Jammu and Kashmir forming segment II. This underground ridge is 65-70 km in width between Ganga and Yamuna across Dehradun and is expected at a depth of 2.5 km.
The structures to the east and west of this ridge are totally different. Palaeozoic and Mesozoic sediments in Lesser Himalaya are almost absent, except the Tal Phosphorite of Cambrian age and a Permian local transgression restricted to segment I only. The segment II is mainly marine repre. sented by Subathu, Dagshai, Kasauli, Murrees, Dharamsalas, Nahans and even Lower Siwaliks, in a NNW - SSE trending foot hill belt of 120-20 km upto Yamuna. Most of these formations are fossiliferous. To the east of it, only fresh water fluvial - deltaic sediments of Middle and Upper Siwaliks, are developed in the form of a linear belt of 20 km width. Mineral occurrences of evaporites like gypsum of Ramban and Common salt of Mandi (segment II) are totally absent in segment I. The phosphorite of Tals near Mussoorie continues to the SSW in Haryana and Rajasthan at 7 localities in a linear belt of 1200 km in length. Similar exposure of mineralized zones of base metals, copper ores of Khetri, Lead and Zinc of Zawar and Ambamata in Gujarat are located and closely linked with this DHH. The mighty sedimentary sequence of Vindhyan System is restricted by the Aravalli along DHH and so no older basement in western Rajasthan (Fig.1). The DHH restricts the Indus flysch and volcanics in the west in Ladakh.
The DHH forms a western limit of newly created Indo - China Plate (Fig.2). It is originating from Carlsberg Ridge in Indian Ocean, runs as a submarine ridge via Chagos Archipelago, Male, Lakshdweep and Gulf of Cambay along the West Coast of India, Ahmedabad, Ajmer, Delhi (Aravalli Range) and continues NNE as an underground ridge between Delhi and Hardwar and further below Himalayas via Harsil, It forms the NW limit of Tibetan Plateau, runs along the Astin Tagh (Altyn Tagh) and Qilian mountain, Huang Hwo (Yellow) river for sometime and then following to the east of Khingan mountain and finally Okhotsk sea where it meets the al- ready well established plate boundary from Pacific side.
India and Australia are divided by another ridge which separates from south eastern Indian Ridge to reach Andaman and Nicobar Islands and Ninety Degree East Ridge.
The western periphery of this plate boundary, the fundamental fracture is forming a well-controlled water divide from Gulf of Cambay to Okhotsk sea. The eastern part is drained by Chambal, Yamuna, Ganga, Brahmputra, Yangsikiang, Tsekiang, Huang Hwo, etc., flowing to the east, and the west- ern part is drained by Indus, Chenab, Sutlej, Luni and Sabramati. Only exception is Yamuna which originates at the western limit, follows it along the western margin of DHH, but cuts across the western margin of DHH, in Delhi to become a tributary of Ganga. The originating points of major rivers Indus, Chenab, Sutlej, Yamuna, Ganga and Brahmputra lie within lOO km radial distance and pattern in higher Himalayan areas. Rann of Kutch, Thar Desert of Rajasthan, Sambhar Salt Lakes region. cold desert of Ladakh, Takla Makan Desert of Sinkiang province of China and Gobi Desert of Mongolia are situated just adjacent and limited by this boundary to the west and northwest. Eastern side is generally plateau - Deccan Plateau, Malwa Plateau, Marwar Plateau, Tibetan Plateau, etc. Recurrences of several shallow earthquakes are quite frequent on this boundary. A few to mention are Uttarkashi 1991, Mahatastra-Latur 1993, Sinkiang province 1975 and NE China 1976. The Cenozoic/Cretaceous volcanism along the West Coast of India, Gu1f of Cambay, Gujarat, Rajasthan, Tibet, China and Okhotsk-west coast is a testimony of large scale lava flows of volcanic eruptions along this boundary at that time.
The Indo-Chinese Plate/Continent is still moving in NNE direction and is responsible for the natural hazards throughout this belt in the form of minor and major earthquakes, volcanic movement or ascent of magma upwards, large scale subsidences leading to slope failures, earth flows, mud flows, debris flows, changes in river courses, accelerated river bank erosion and sheet erosion in the entire belt.
Qureshy (1971,p.170) while preparing the bouguer anomaly map of UP Himalaya shows the closure of contours right at Harsil and flexuring between Dehradun and Hardwar. The eastern flank of Delhi-Hardwar-Harsil Ridge passes through this flexure and closure precisely.
It is interesting to note that the epicentre of the main shock of Kinnaur Earthquake of 19th January, 1975 (Khattri et al., 1978; Banghar, 1976) lies exactly on the western limit of DHH. The epicentres of aftershocks are also falling along this feature only. This feature is well marked by a normal north to southwesterly dipping fault (Sharma, 1978) between Kaurik~Sumdoh and Sangla. Sutlej and Spiti follow it for quite a long distance and the landslides along the DHH ridge in Pooh area are closely linked to the movement of DHH. Khattrt et al. (1978) have named this fault as Chaugo-Kaurik Fault. The fault is responsible for brecciation, hot springs and gypsum encrustations aligned linearly. This fault and the DHH restrict the Spiti Basin to its west and Badrinath-Harsil to its east. Further north in Tibet- China, a large number of earthquakes falling on this boundary have struck.
A new concept has been proposed about the northern boundary of Indo-Australian Plate which was supported by geomorphic feature and also by geophysical aspects. The frequent occurrences of earthquakes, Tertiary volcanism and related hazards are mainly along this boundary.
Banghar.A.R.. 1976, Mechanism solution of the Kinnaur (H.P.) earthquake: Himalayan Geology, v.6, p. 75-80.
Gansser,A., 1964, Geology of the Himalayas: Interscience, New York, 289p.
Kaila, K.L. and H. Narain, 1976, Evolution of the Himalaya based on seismotectonics and deep seismic soundings. Himalayan Geology Seminar: G.S.I. Miscellaneous Publication Number 41 (1981), p.1-39.
Khattri, K.N., Rai, K., Jain, A.K., Sinval. H., Gaur, V.K. and R.S. Mithal, 1978, The Kinnaur earthquake, H.P., India of 19th January, 1975: Tectonophysics. v.49, p.1-21.
Molnar,P., 1986, The geologic history and structure of the Himalaya: American Scientist, v.74, p.144-154.
Qureshy, M.N. ,1971, Geophysical investigation in the Himalaya: Himalayan Geology, v.l, p.165-177.
Raiverman, V., 1986, Sedimentation pattern and its controlling factors in the Cenozoic basins of the Indian Subcontinents : ONGC Bulletin, v.23, no), 1, p.1-16.
Sinha, A.K.,1 989, Geology of Higher Central Himalaya: John Wiley & sons, Chichester, 123p.
ABOUT THE AUTHOR
Dr. Devendra Pal, scientist E-II has worked in Ladakh, Kashmir, Jammu- Batote, Kangra-Mandi-Solan areas, Doon Valley, Garhwal and Kumaun Himalaya. He alongwith his associates worked out a typical miogeo- synclinal set up in Indus Zone of Ladakh and worked on the nature of Main Boundary Fault and tear faults from Riasi to Tanakpur . He has tried to develop a new concept of Himalayan uplift and its implications on natural hazards. His main interest is in Quaternary Himalayan tectonics, global climatic changes, Neotectonics, earthquakes, natural hazards like landslides. Subsidences, erosion, cloud burst and flashfloods. He has thirty five research papers to his credit.<
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Manuscript received : November 5,1993
Manuscript accepted : March 2, 1994.