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Himalayan transverse faults and folds and their parallelism with subsurface structures of north indian plains—discussion
Tecfonophysics, 56 (1979) 299-303 0 Elsevier Scientific Publishing Company,
299 Amsterdam
-Printed
in The Netherlands
HIMALAYAN TR~SVERSE FAULTS AND FOLDS AND THEIR PARALLELISM WITH SUBSURFACE STRUCTURES OF NORTH INDIAN PLAINS - DISCUSSION
K.S. MISRA Centre of Studies in Resources Engineering, bay-400076 (India) (Received
May 21, 1978; accepted
Indian Institute of Technology,
for publication
October
Powai, Bom-
9, 1978)
A spectacular exposition of regional transverse faults and folds in the Himalayas has been made by Landsat imageries of the northwestern Himalayas, and the present author believes that these faults and folds are the manifestations of the last major tectonic deformation in the complete orogeny of the Himalayas. The present study, therefore, does not support Valdiya (1976) who concluded that transverse faults and folds represent undersurface extensions of peninsular erogenic trends, such as the Satpura, Bundelkhand and Aravalli. The present work on a mosaic of six frames of Landsat imageries, has brought out an open folding on a NE-SW axis and development of several tears and faults, parallel to the fold axis as shown in the enclosed geological map of the northwestern Himalayas (Fig. 1). The folding on the NE-SW axis of the Siwalik Group of rocks, of Helvetian to Cromarian age, and the still younger Main Boundary Fault, indicates the extreme youth if this fold episode during the later part of the Quaternary Era. The folds related to this tectonic deformation are of very open nature and their axial planes show a gradual fanning out from ENE-WSW in the northwestern part to NNW-SSE in the southeastern part. The complicated outcrop pattern and development of culminations and depressions on earlier folds parallel to Himalayan axis is also interpreted as being due to this fold movement. Several earlier workers have also described the last phase of tectonic movement on N-S to NE-SW axes from various isolated areas in the Himalayas. Ray and Naha (1971) noted the last folding on a N-S axis in the Simla area and interpreted the pear-shaped pattern of the Jutogh thrust to be due to this folding. Munshi et al. (1972) recognised the last folding on a NNE-SSW axis in the SomeshwarDwarahat area and believed that the plunging of the Dunagiri anticlinal structure in a SSE direction and the Someshwar anticlinal structure in a SSW direction, is because of this fold episode. Similar such open folds are described in the Chail area by Fuchs (1975) and by Bordet
300
P
n f Ic
301
(1973) in the Arun valley in Nepal, Jangpangi (1974) from the Bhutan Himalayas and by Das et al. (1971) from the Arunachal Himalayas. It is thus clear beyond doubt that this fold movement has not only affected the northwestern Himalayas, but also the eastern extension in Nepal, Bhutan and the Arunachal Himalayas. The present author differs with Valdiya (1976) because of three significant considerations. (1) If the transverse folds and faults were due to earlier subsurface extensions of Peninsular erogenic trends, they would have been lost or severely affected by major folding episodes, parallel to the main Himalayan axis. On the contrary, the transverse folds and faults are best preserved and are not at all affected by the fold episodes parallel to the Himalayan axis. (2) Due to their regularity in fold pattern all along the length of the Himalayas from Kashmir to Arunachal Pradesh, and a clearcut superposition on earlier folds and consequently generating culmination and depression in them. (3) Only the NE-SW trend of Aravalli is transverse to the Himalayan axis and if it should have given rise to transverse folds and faults at all, they would have been concentrated locally in the area where the probable subsurface trend of Aravalli meets the Himalayan trend. The Satpura trend is almost E-W and there is no likelihood of this trend affecting the Himalayas. Regional studies indicate that the Himayalas are overthrust towards the south, the Iranian arc is overthrust towards the east and the Burmese arc is overthrust westwards, on the Indian plate with marked convex trends. It is generally believed that the compressive forces responsible for the Himalayan orogeny have mainly come from a SW direction due to the northerly movement of the Indian plate and its ultimate collision with the southeast margin of Asia (Dietz and Holden, 1970). The compressive forces responsible for causing the last tectonic movement are believed by the present author to have come from ESE and WNW directions, earlier unknown in the Himalayas. The sequence of events thus could be that the northerly movement of the Indian plate resulted in the folding of Himalayan rocks on ENE-WSW axes and their overthrusting towards the south in the early part of the orogeny. Continued accumulation of stresses later resulted not only in breaking of the ranges at Pamir, syntaxis in the west and the Assam wedge in the east, giving rise to the Iranian and Burmese arcs, but also over-thrusting of the two arcs in east and west directions, respectively. The simultaneous overthrusting of two arcs compressed the Himalayan rocks and their folding on NE-SW axis, at a much later part of the Himalayan orogeny. REFERENCES Bordet, I’., 1973. On the position of the Himalayan Main Thrust within Nepal Himalayas. Proc. Sem. Geodyn. Himalayan Region, Nat. Geophys. Res. Inst. Hyderabad, pp. 148155. Das, A.K., Bakliwal, P.C. and Dhoundial, D.P., 1971. A brief outline of the geology of parts of Kameng Distt. NEFA. Sem. Geol. Stud. Himalayas, Geol. Surv. India, Calcutta, pp. 6-7. Diets, R.S. and Holden, J.C., 1970. Reconstruction of Pangea. J. Geophys. Res., 75 (26).
302 Fuchs, G., 1975. Contribution to the geology of the northwestern Himalayas. Abh, Geoi. Bundesanst., 32: l-59. Jangpangi, B.S., 1974. Stratigraphy and tectonics of parts of the Eastern Bhutan. Himalayan Geol., 4: 117-136. Munshi, S.K., Misra, K.S. and Merh, S.S., 1972. A note on the structure of the Krol nappe rocks in Someshwar-Dwarahat region in Amora district. U.P. Abstr. Proc. Indian. Sci. Congr., Part 3, p. 59. Ray, S.K. and Naha, K., 1971. Structure and metamorphic history of the “Simla Klippe” a Summary. Himalayan Geol., 1: l-24. Valdiya, K.S., 1976. Himalayan transverse faults and folds and their parallelism with subsurface structures of north Indian plains. Tectonophysics, 32: 353-366. --_-
HIMALAYAN TR~SVERSE FAULTS AND FOLDS AND THEIR PARALLELISM WITH SUBSURFACE STRUCTURES OF NORTH INDIAN PLAINS - REPLY TO K.S. MISRA
K.S. VALDIYA Department
of Geology, Kumaun University, Nainital 263002
(India)
(Received September 8, 1978; accepted for publication October 9, 1978)
In my reply to the comments of S. Sinha Roy (Valdiya, 1979) I thought that I had made it clear that it is only the first-generation isoclinal, recumbent or reclined folds discernible in the crystalline nappes which are older and presumably Precambrian in age and that the NE-SW trending (in Kumaun) open, upright and plunging folds developed practically in all the lithotectonic units are quite young; later than the main Himalayan erogenic phase. It should have been obvious to Misra from my repeated statement pointing out and emphasizing the offsetting of such young features as the Main Boundary Thrust and Upper Siwalik formation that many of the transverse faults are very young. However, I feel that these faults represent reactivation and regeneration of the Precambrian structures and grains now aligned transverse to the Himalayan trend. The activation-regeneration being quite late (later than main Himalayan revolution), they do not exhibit departure from their original trend, having parallelism with those of the Peninsular shield. The forces responsible for the generation of the younger set of folds (which have not been obliterated by later movements) are attributed to the movements causing reactivation-regeneration of the faults. The transverse structures in the eastern sector of the Himalaya reflect the structural trends in the Satpura and Assam plateau, and not the Aravali. REFERENCES Misra, K.S., 1979. Himalayan transverse faults and folds and their parallelism with subsurface structures of North Indian plains - discussion. Tectonophysics, 56: 299-302.
299 Amsterdam
-Printed
in The Netherlands
HIMALAYAN TR~SVERSE FAULTS AND FOLDS AND THEIR PARALLELISM WITH SUBSURFACE STRUCTURES OF NORTH INDIAN PLAINS - DISCUSSION
K.S. MISRA Centre of Studies in Resources Engineering, bay-400076 (India) (Received
May 21, 1978; accepted
Indian Institute of Technology,
for publication
October
Powai, Bom-
9, 1978)
A spectacular exposition of regional transverse faults and folds in the Himalayas has been made by Landsat imageries of the northwestern Himalayas, and the present author believes that these faults and folds are the manifestations of the last major tectonic deformation in the complete orogeny of the Himalayas. The present study, therefore, does not support Valdiya (1976) who concluded that transverse faults and folds represent undersurface extensions of peninsular erogenic trends, such as the Satpura, Bundelkhand and Aravalli. The present work on a mosaic of six frames of Landsat imageries, has brought out an open folding on a NE-SW axis and development of several tears and faults, parallel to the fold axis as shown in the enclosed geological map of the northwestern Himalayas (Fig. 1). The folding on the NE-SW axis of the Siwalik Group of rocks, of Helvetian to Cromarian age, and the still younger Main Boundary Fault, indicates the extreme youth if this fold episode during the later part of the Quaternary Era. The folds related to this tectonic deformation are of very open nature and their axial planes show a gradual fanning out from ENE-WSW in the northwestern part to NNW-SSE in the southeastern part. The complicated outcrop pattern and development of culminations and depressions on earlier folds parallel to Himalayan axis is also interpreted as being due to this fold movement. Several earlier workers have also described the last phase of tectonic movement on N-S to NE-SW axes from various isolated areas in the Himalayas. Ray and Naha (1971) noted the last folding on a N-S axis in the Simla area and interpreted the pear-shaped pattern of the Jutogh thrust to be due to this folding. Munshi et al. (1972) recognised the last folding on a NNE-SSW axis in the SomeshwarDwarahat area and believed that the plunging of the Dunagiri anticlinal structure in a SSE direction and the Someshwar anticlinal structure in a SSW direction, is because of this fold episode. Similar such open folds are described in the Chail area by Fuchs (1975) and by Bordet
300
P
n f Ic
301
(1973) in the Arun valley in Nepal, Jangpangi (1974) from the Bhutan Himalayas and by Das et al. (1971) from the Arunachal Himalayas. It is thus clear beyond doubt that this fold movement has not only affected the northwestern Himalayas, but also the eastern extension in Nepal, Bhutan and the Arunachal Himalayas. The present author differs with Valdiya (1976) because of three significant considerations. (1) If the transverse folds and faults were due to earlier subsurface extensions of Peninsular erogenic trends, they would have been lost or severely affected by major folding episodes, parallel to the main Himalayan axis. On the contrary, the transverse folds and faults are best preserved and are not at all affected by the fold episodes parallel to the Himalayan axis. (2) Due to their regularity in fold pattern all along the length of the Himalayas from Kashmir to Arunachal Pradesh, and a clearcut superposition on earlier folds and consequently generating culmination and depression in them. (3) Only the NE-SW trend of Aravalli is transverse to the Himalayan axis and if it should have given rise to transverse folds and faults at all, they would have been concentrated locally in the area where the probable subsurface trend of Aravalli meets the Himalayan trend. The Satpura trend is almost E-W and there is no likelihood of this trend affecting the Himalayas. Regional studies indicate that the Himayalas are overthrust towards the south, the Iranian arc is overthrust towards the east and the Burmese arc is overthrust westwards, on the Indian plate with marked convex trends. It is generally believed that the compressive forces responsible for the Himalayan orogeny have mainly come from a SW direction due to the northerly movement of the Indian plate and its ultimate collision with the southeast margin of Asia (Dietz and Holden, 1970). The compressive forces responsible for causing the last tectonic movement are believed by the present author to have come from ESE and WNW directions, earlier unknown in the Himalayas. The sequence of events thus could be that the northerly movement of the Indian plate resulted in the folding of Himalayan rocks on ENE-WSW axes and their overthrusting towards the south in the early part of the orogeny. Continued accumulation of stresses later resulted not only in breaking of the ranges at Pamir, syntaxis in the west and the Assam wedge in the east, giving rise to the Iranian and Burmese arcs, but also over-thrusting of the two arcs in east and west directions, respectively. The simultaneous overthrusting of two arcs compressed the Himalayan rocks and their folding on NE-SW axis, at a much later part of the Himalayan orogeny. REFERENCES Bordet, I’., 1973. On the position of the Himalayan Main Thrust within Nepal Himalayas. Proc. Sem. Geodyn. Himalayan Region, Nat. Geophys. Res. Inst. Hyderabad, pp. 148155. Das, A.K., Bakliwal, P.C. and Dhoundial, D.P., 1971. A brief outline of the geology of parts of Kameng Distt. NEFA. Sem. Geol. Stud. Himalayas, Geol. Surv. India, Calcutta, pp. 6-7. Diets, R.S. and Holden, J.C., 1970. Reconstruction of Pangea. J. Geophys. Res., 75 (26).
302 Fuchs, G., 1975. Contribution to the geology of the northwestern Himalayas. Abh, Geoi. Bundesanst., 32: l-59. Jangpangi, B.S., 1974. Stratigraphy and tectonics of parts of the Eastern Bhutan. Himalayan Geol., 4: 117-136. Munshi, S.K., Misra, K.S. and Merh, S.S., 1972. A note on the structure of the Krol nappe rocks in Someshwar-Dwarahat region in Amora district. U.P. Abstr. Proc. Indian. Sci. Congr., Part 3, p. 59. Ray, S.K. and Naha, K., 1971. Structure and metamorphic history of the “Simla Klippe” a Summary. Himalayan Geol., 1: l-24. Valdiya, K.S., 1976. Himalayan transverse faults and folds and their parallelism with subsurface structures of north Indian plains. Tectonophysics, 32: 353-366. --_-
HIMALAYAN TR~SVERSE FAULTS AND FOLDS AND THEIR PARALLELISM WITH SUBSURFACE STRUCTURES OF NORTH INDIAN PLAINS - REPLY TO K.S. MISRA
K.S. VALDIYA Department
of Geology, Kumaun University, Nainital 263002
(India)
(Received September 8, 1978; accepted for publication October 9, 1978)
In my reply to the comments of S. Sinha Roy (Valdiya, 1979) I thought that I had made it clear that it is only the first-generation isoclinal, recumbent or reclined folds discernible in the crystalline nappes which are older and presumably Precambrian in age and that the NE-SW trending (in Kumaun) open, upright and plunging folds developed practically in all the lithotectonic units are quite young; later than the main Himalayan erogenic phase. It should have been obvious to Misra from my repeated statement pointing out and emphasizing the offsetting of such young features as the Main Boundary Thrust and Upper Siwalik formation that many of the transverse faults are very young. However, I feel that these faults represent reactivation and regeneration of the Precambrian structures and grains now aligned transverse to the Himalayan trend. The activation-regeneration being quite late (later than main Himalayan revolution), they do not exhibit departure from their original trend, having parallelism with those of the Peninsular shield. The forces responsible for the generation of the younger set of folds (which have not been obliterated by later movements) are attributed to the movements causing reactivation-regeneration of the faults. The transverse structures in the eastern sector of the Himalaya reflect the structural trends in the Satpura and Assam plateau, and not the Aravali. REFERENCES Misra, K.S., 1979. Himalayan transverse faults and folds and their parallelism with subsurface structures of North Indian plains - discussion. Tectonophysics, 56: 299-302.