Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India

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1 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India Chaitra Dhar Taye and Raghupratim Rakshit Department of Applied Geology, Dibrugarh University, Dibrugarh, Assam ABSTRACT In the present study we have considered the Tawang River Basin and its subbasins located in the eastern Himalaya, northeastern India. The area under study is bounded on the north by the South Tibetan Detachment System (STDS), on the east by the Main Central Thrust (MCT), and on the south and west by the Bhutan Himalayas. It originates from the Tibet (China) and flows towards southwest direction through India to Bhutan analogously with the major regional structures of the area. The purpose of this investigation is to examine the influence of active structures by applying an integrated study on supportive field evidences, geomorphology, morphotectonics, Digital Elevation Model (DEM) and using topographic map. The measured indices for morphotectonic analysis, viz. Asymmetric Factor (AF=2 to 26), Transverse Topographic Symmetry Factor (T = 0.13 to 0.78), Stream Length gradient index (SL), Basin shape indices (Bs = 0.35 to 0.85) and lineament analysis indicated that the area is tectonically active. Lineament density plots indicate the NNE and NNW stress component and EW trend. From the present investigation, we can assume that the Tawang Chu River itself is flowing through a major anomalous structural or tectonic feature. Moreover, these findings can assist to recognize the potential geo-hazardous areas as the area is tectonically active and sound to regional threat. Keywords: Tawang River Basin, Main Central Thrust (MCT), morphotectonics, lineaments, SL index. INTRODUCTION The Tawang district is the highly mountainous westernmost district of Arunachal Pradesh, northeast India and is situated near the international boundary of both China and Bhutan. These northeastern parts of India belong to the tectonically active regions. The study of morphotectonics is important as the role of active tectonics for evaluating natural hazards as well as for the developmental planning for any region may be projected. Apart from this, studies of Active Tectonics follow a multi-disciplinary approach by integrating information from structural geology, geomorphology, stratigraphy, geochronology and seismology (Pérez-Peña et al., 2010). Whipple (2001, 2004) stated that the active tectonic evolutionary study aims to provide whether the area belongs to steady-state condition or not. The steady state will be reached if landforms are in equilibrium with the denudation processes and this becomes timeindependent (Hack, 1960, 1975), whereas disequilibrium in the erosional system continues until permanency is achieved (Whipple and Tucker, 1999). The Himalaya comprises of many north dipping thrust sheets, which are punctuated by topographic breaks. Northeastern Himalaya experienced many high magnitude 11

2 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit earthquakes in the past century. The active process in the Himalayan orogeny is a dominant factor in the revolutionary changes in the geomorphological aspects in the NE India (Bhatia et al.,1999). Most of the seismicity in the Himalayan region is concentrated along shallow north dipping planes, which indicate under thrusting of the Indian plate beneath the Eurasian plate (Bhatia et al.,1999). The NE India affected by many major earthquakes in the past and earthquakes of Manipur (India, January, 2016) and Mawlaik (Myanmar, April, 2016) are the most recent examples. All the linear tectonic features viz. Main Boundary Thrust (MBT), Main Central Thrust (MCT) and Indus Tsangpo Suture Zone (ITSZ) are mostly associated with the seismic activity in and around the region. Fig. 1: Geological map of the study area (modified after Goswami et al., 2009). In mountainous region like Arunachal Pradesh, the main factor contributing to rock upliftment and their present-day topography is the result of the denudation processes. The river Tawang Chu and Nyamjang Chu are the two major rivers present in the area under study. These two major rivers enter the Tawang district from Tibet in the northeast and flow southwesterly direction to Bhutan in the southwest. This area is covered by Higher Himalayan crystalline rock terrain and the northern part is snow bound with high hills and steep slopes. Due to its difficult topographic nature and snow cover, these areas have received little attention and the morphotectonic characteristics of the Tawang basin have not been investigated. Therefore, this study aims to unravel the active tectonic mysteries of the Tawang basin (Fig. 1) by studying the present morphotectonic characters and lineament analysis. GEOLOGY OF THE AREA Lithostratigraphically, the rocks exposed in the study area belong to Se La Group and Dirang/Lumla Formation. Se La Group is structurally the highest unit, which is separated from the Dirang Formation to the south by Main Central Thrust (MCT) (Kesari, 2010). It derived its name from the Se La pass in West Kameng district (Das et al., 1975). The predominance of migmatites, lit-par-lit injections, high grade of metamorphism and profuse intrusions of tourmaline granite characteristically differentiate this sequence from the structurally underlying Dirang Formation. This Group may be considered to represent an early Palaeoproterozoic sequence (Wang, 1986). The study area is bounded by South Tibet Detachment (STD) in the north and Main Central Thrust (MCT) in the south. The MCT is well defined in north of Dirang in the West Kameng district where the rocks of the Bomdila Group are truncated with conspicuous presence of moderately dipping thrust (Bhusan, 1999).

3 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp METHODOLOGY To understand the morphotectonic characteristics of the Tawang Basin, geomorphic index was calculated by using topographic maps at scale 1: 50,000 of the Survey of India Toposheet numbers 78M/9,10,13,14,15; 83A/1,2,3 and standard methods of digitization, image to image registration by selecting proper Ground Control Points (GCPs). Profiles have been made by using Digital Elevation Map (DEM) of 30m resolution of the study area (Earthexplorer, USGS). The Lineament density plot or Rose Diagram for Macro and Microlineaments are plotted using the Rozetta software. Global Mapper 15 software has been used for making the profiles for elevation studies. An attempt has also been made to correlate the results with field observations. RESULTS AND INFERENCES The morphotectonic parameters that are used for delineation of the morphological and Tectonic characteristics in the study have their own prospective. For the comparative and convenient study, the whole Tawang Basin is divided into four divisions as N1, N2, S1 and S2 respectively. The results of the morphotectonic parameters for all the studied basins are given in Table-1. Transverse topographic symmetry factor: This quantitative index is calculated from the equation T = Da/Dd, where Da is the distance from the midline of the drainage basin to the midline of the active meander belt and Dd is the distance from the midline to the basin divide (Cox, 1994). For a perfectly symmetric basin T = 0 while T increases and approaches a value of 1.0 as asymmetry increases. The values of T, in the area under study, ranges between 0.13 to 0.77 (Table-1). This range values indicate that most of the basins of the area have greater asymmetry and some of them show moderate to low asymmetry. Moreover, most of the studied basins are showing NW-NNW and S-SE tilting direction. The major tilting trends for N1 and N2 divisions show SE and NW, SSE- SSW tilting basins; however, the major tilting trends for S1 and S2 divisions have NNW and NE-NNW tilting pattern. Asymmetry factor: The lateral shifting of the drainage basin can also be explained by asymmetry factor (AF). Asymmetry factor is calculated for each basin to determine whether any tectonic deformation or tilting exist in the area. The asymmetry factor of the basin is calculated using formula as AF = 100 (Ar/ At). Where Ar = Area of the basin belongs to right trunk of the stream; At = Total area of basin and absolute AF values are indicative of active tectonic activity in the whole study area. The tilting directions of the basin are similar to that of the T values. In order to avoid possible confusions absolute values of AF are calculated by AF = 50- (Ar x 100/ At). The absolute AF value with an arrow indicating the asymmetry direction in the study area is presented in Fig. 2. Pérez-Peña et al. (2010) classified AF absolute values in four classes: I. Symmetric basins (<5), II. Gently asymmetric basins (5 10), III. Moderately asymmetric basins (10 15) and IV. Strongly asymmetric basins (>15). The AF values of the Tawang basin mostly inferred gently to strongly asymmetric basins in few cases show symmetric basins. Moreover, 13

Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit in comparison with S1 divisions N1, N2 and S2 has higher AF values having 26.41, 24.

4 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit in comparison with S1 divisions N1, N2 and S2 has higher AF values having 26.41, and respectively (Table- 1). Fig. 2: The Asymmetry Factor (AF) of all the sub basins indicating tilting direction. Northern and Southern part of the Tawang Chu River is subdivided into N1, N2 and S1, S2 respectively. Profile lines of 6 (six) NW-SE and 2 (two) WSW-ENE (X-X/ and Y-Y/) along Northern and Southern sides of Tawang Chu River (Major structures are after Yin et al. 2010). MCT- Main Central Thrust, KZT- Kakhtang-Zimithang Thrust, CNF- Cona Normal Fault. Basin shape parameters: The basin shape can be delineated by two parameters viz. Basin elongation ratio (Bs) and Basin circularity ratio (Bc). Elongation ratio of a basin can be computed using the formula: Bs= Bl/Bw, Where Bl is the length of a basin measured from the highest point, and Bw is the width of a basin measured at its widest point. In tectonically active areas the relatively younger drainage basins tend to be elongated in shape, normal to the topographic slope of a mountain (Bull and McFadden, 1977; Ramírez-Herrera, 1998). For an elongated basin Bs ~ 0; Circular basins have Bs=1. Circularity ratios of the basins are calculated by the formula: Bc = 4πA / P 2, where A is the basin area of the same basin order, and P is the basin perimeter of the same basin. The value of circularity ratio varies from 0 (in elongate) to 1 (in a circle). These two parameters together are very useful in determining the basin shapes that depend on the active tectonics in the region. The elongation ratio (Bs) values of the study area range from 0.35 to 0.85 whereas the circularity ratio (Bc) shows the range from 0.4 to 0.9 (Table-I). Though elongation ratio does not show desirable result but together with circularity ratio we can interpret the basin characteristics (Bull and McFadden, 1977). The study area is consisting mostly of semielongated basins with few show semi-circular pattern. Stream length gradient index: The formula SL = (ΔΗ/ΔL) L is used to calculate stream length gradient index, where ΔΗ/ΔL is the stream gradient at a specific site in the channel (ΔΗ is the change in elevation of

5 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp the reach and ΔL is the length of the reach) and L is the total channel length from the point of interest where the index is being calculated upstream to the highest point on the channel (Hack, 1973; Keller and Pinter, 2002). SL index show a relationship between potential tectonic activity, rock resistance, topography and length of the stream (Azor et al., 2002; Keller and Pinter, 2002; Zovoili et al., 2004). In the present study the SL index values are calculated in different segments of each basin with general points has been taken into account and some SL values show anomalistic relation against the river profile (Fig. 3). The studied basin shows SL values of high to low anomalous zones (Table-2). Most of the high and mid anomalous zones are concentrated near the Tawang Chu River along NE-SW trend. When the Low Anomalous zones are taken into consideration, they are laid in low elevated areas, compare to its average basin elevation, with respect to the stream profile, which might have local structural or tectonic relationship. Table-1: Results of the morphometric parameters T, AF, Bs and Bc along with basin number and basin order Basin No Order T AF Bs Bc Basin No Order T AF Bs Bc N1 N2 B 1 3RD B12 3RD B 2 3RD B13 3RD B 3 5TH B14 3RD B 4 3RD B15 4TH B 5 4TH B16 3RD B 6 4TH S B17 3RD B 7 4TH B18 3RD B 8 3RD B19 3RD B 9 3RD B20 4TH B10 3RD B21 4TH B11 3RD B22 3RD B29 4TH B24 3RD B31 3RD B25 4TH B32 5TH S2 B26 3RD B 33 4TH B27 4TH B36 4TH B28 3RD Lineament analysis: The study area is also important to unravel the mysteries of differential tectonic activities in different regions and also to predict the stress direction as well. The area under study comprises of both Macro- (>3 km) and Micro- (<3km) Lineaments (Fig. 4). The Lineament is studied in all four N1, N2, S1 and S2 divisions respectively. Lineaments of N1division show SE trend and few aligned in Northern direction. The Macro-Lineaments follow similar pattern but the Micro-Lineaments indicate Easterly to ESE trend. Although, divisions of N2 Lineaments that indicate Southerly trends both in Macro- and Micro-, some of the other 15

6 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit Lineaments follow Easterly trend. For overall Northern Side the Macro-Lineaments show SE trend and Micro-Lineaments show Easterly to SE trends (Figure-5A). However, in S1 division most of the lineaments show northerly trend and Macro-Lineaments follow NNE pattern but the Micro-Lineaments indicate NNW trend. Again in S2 division both in Macro- and Micro- Lineaments indicate N-NNW trends. Some of the other Lineaments follow NE trend mainly in Macro-Lineaments (Fig. 5B). The distribution of Micro Lineaments might be the result of the EW anomalous force and the extended effects of the Se La Synclinorium in the region. Fig.3: SL Index values (red lines) of some basins and the relation with their river profile (blue) plots showing anomalistic outcomes. Table-2: SL Values are grouped into 3 (three) zones depending on calculated values Range HIGH ANOMALOUS ZONE S.L. values > 3000 MID ANOMALOUS ZONE S.L. values LOW ANOMALOUS ZONE S.L. values <500 Basins 1,3,5, 6, 7, 9, 12,15, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 30, 32, 33, 35, 36 1, 2, 7, 9, 13, 17, 18, 19, 20, 21, 25, 26, 27, 28, 29, 30, 32 12, 15, 16, 21, 25, 35, 36

Open access e-journal Earth Science India eissn: 0974 8350 Vol. 11 (I), January, 2018, pp. 11-22 http://www.earthscienceindia.info/ Fig.

7 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp Fig. 4: Lineament map of the study area demarcating macro and micro lineament and anomalous zones. The profiles: Apart from the morphotectonic parameters, the elevation differences along 6 (six) NW- SE Profile Lines, 2 (two) WSW-ENE profile lines X-X / and Y-Y / along Northern and Southern sides of Tawang Chu River (Fig. 2) have been studied. The profile lines AA', BB' and CC' (Fig. 6) shows that the northeastern block of the Basin (i.e. bounded by Tawang Chu and Nyukcha Rong Chu Rivers) has higher elevation on NE side of the block and lower elevation on SW side compare to the other blocks. Across the Nyukcha Rong Chu River there is change in tectonic activity and stress direction may shift the lineaments more towards southern trend. This might also cause the shifting of the river course on that point. This can be proved by further study of the upliftment rate in this area, which is beyond the scope of this work. Profile Lines DD', EE' and GG' (Fig. 7) indicate that the Northern side of Tawang Chu River has greater elevation compared to the Southern side and the relation holds well though the elevation on both sides decreases downstream. The two WSW-ENE profile lines (X-X / and Y-Y / ) inferred that the whole basin is tilted towards the downstream of the Tawang Chu River (Fig. 8). 17

Fig. 5: The Lineament density plot for Macro- and

8 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit Fig. 5: The Lineament density plot for Macro- and Micro-Lineaments of the study area. A) Northern part and B) Southern part.

Open access e-journal Earth Science India eissn: 0974 8350 Vol.

9 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp Fig. 6: Profile lines of AA', BB' and CC' of the study area showing the relations of A, B and C Blocks. Fig. 7: Profile lines of DD', EE' and GG' of the study area showing the relations of B and C Blocks. 19

10 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit Fig. 8: Profile lines of X-X / and Y-Y / of the study area showing the relations of different Blocks. The river profile of Tawang Chu has a significant knick-point, which indicates that in the studied basin, the upstream of the knick point has greater upliftment rate compare to the downstream. This knick-point is found to be near to the confluence of both Mago Chu and Nyukcha Rong Chu Rivers (Fig. 9). This is evidence from the fact that the northeastern block (Block A) has higher upliftment rate comparing to the other blocks (Block B & C), which is also visible in the field (Fig. 10). The confluence may act as convergence point of two different trending features. It is causing the pop-up of the enclosed block. Fig. 9: The profile of Tawang Chu river indicating significant knick-point along with the field photographs of confluence of both Mago Chu and Nyukcha Rong Chu Rivers.

Open access e-journal Earth Science India eissn: 0974 8350 Vol. 11 (I), January, 2018, pp. 11-22 http://www.earthscienceindia.info/ Fig. 10: Field photograph showing different blocks viz.

11 Open access e-journal Earth Science India eissn: Vol. 11 (I), January, 2018, pp Fig. 10: Field photograph showing different blocks viz. Block A, Block B & Block C in the study area. These might indicate that the river Tawang itself behaving as a boundary line between Northern and Southern sides and it is emerging as a structural feature trending NE-SW. Considering only Northern and Southern side, it is inferred that Northern side show SE trend in both Macro- and Micro-lineaments, whereas the other side show Northerly trend. Enhancing the presence of the feature along the river, which may be a possible emerging fault (or thrust) parallel to the MCT. The lineaments and the anomalous zones show direct relationship and overlapped along the trend of the Lineaments. CONCLUSION The study of morphotectonic parameters of Tawang basin concludes that the Tawang basin is tectonically active. The Transverse Topographic Symmetry Factor (T) and Asymmetry Factor (AF) indicate activeness of differential tectonic upliftment in the region as inferred by the tilting of the basins. The major concluding points can be summarized as: The high anomalous zones observed in S.L. plots to be concentrated along both sides of the Tawang Chu River. The lineament studies indicate that the effect of NNE to NNW stress directions in the study area. Lineaments also provided evidences for existence of regional EW trending feature, above which the Tawang Chu River is flowing. The profiles give the indication that though the whole basin is tilted towards SW direction. The Northeastern Block bounded by the two rivers and the confluence point shows the major Knick-point for the Tawang Chu River. The northeastern Block is uplifting at greater rate and causing change in course direction of the Mago Chu River to the Tawang Chu River. The Tawang Chu River is itself flowing through a structural feature causing difference in elevation and upliftment rate in the north and south of the river. This is probably a 21

12 Morphotectonic Study of Tawang River Basin, Tawang District, Arunachal Pradesh, NE India: Taye and Rakshit blind Fault or Thrust which can be the next major tectonic feature in the region. The tectonic features in the region are complex and needs more detail study to unravel the mysteries. REFERENCES Azor, A., Keller, E. A.and Yeats, R. S. (2002) Geomorphic indicators of active fold growth: South Mountain Oak Ridge anticline, Ventura basin, southern California. Geol. Soc. Amer. Bull., v.114 (6), pp Bhatia, S. C., Kumar, M. R. and Gupta, H. K. (1999) A probabilistic seismic hazard map of India and adjoining regions. Annals of Geophy., v. 42(6), pp Bhusan, S. K. (1999) Reappraisal of the geology between the MBF and the MCT in western Arunachal Pradesh. In: P. K.Verma (ed.) Geological studies in the Eastern Himalayas, Pilgrim Books Pvt. Ltd., Delhi, pp Bull, W. B. and McFadden, L. (1977) Tectonic geomorphology north and south of the Garlock fault, California. In: D. O. Dohering (ed.) Geomorphology in Arid Regions, Geomorphology publication, State University of New York, Binghamton., pp Cox, R. T. (1994) Analysis of drainage basin symmetry as a rapid technique to identify areas of possible Quaternary tilt-block tectonics: an example from the Mississippi Embayment. Geol. Soc. Amer. Bull., v.106 (5), pp Das, A. K., Bakliwal, P. C. and Dhoundial, D. P. (1975) A brief outline of the geology of parts of Kameng district, NEFA. Geol. Sur. Ind. Misc. Pub., v.24(1), pp Goswami, S., Bhowmik, S. K. and Dasgupta, S. (2009) Petrology of a non-classical Barrovian inverted metamorphic sequence from the western Arunachal Himalaya, India. J. Asian Earth Sc., v.36, pp Hack, J. (1960) Interpretation of erosional topography in humid temperate regions. Amer. J. Sc., v.258- A, pp Hack, J. (1975) Dynamic equilibrium and landscape evolution. In: W. Melhorn and R. Flemal (eds.) Theories of landform development, George Allen & Unwin, pp Hack, J. T. (1973) Stream-profile analysis and stream-gradient index. U.S.G.S. J of Res., v.1(4), pp Keller, E. A. and Pinter, N. (2002) Active tectonics: earthquakes, uplift, and landscape. 2nd ed. New Jersey, Prentice Hall, Molnar, pp Kesari, G. K. (2010) Geology and mineral resources of Arunachal Pradesh. Geol. Sur. Ind. Misc. Pub., v.30 (IV), 54 p. Pérez-Peña, J. V., Azor, A., Azañón, J. M. and Keller, E. A. (2010) Active tectonics in the Sierra Nevada (Betic Cordillera, SE Spain): Insights from geomorphic indexes and drainage pattern analysis. Geomor., v.119, pp Ramírez-Herrera, M. T. (1998) Geomorphic assessment of active tectonics in the Acambay Graben, Mexican volcanic belt. Ear. Surf. Proc. and Land., v.23, pp Wang, H. (1986) Geotectonic Development. In: The Geology of China, Oxford Monograph and Geology and Geophysics, v.3, pp Whipple, K. (2001) Fluvial landscape response time: how plausible is steady-state denudation? Amer. J. Sc., v.301, pp Whipple, K. (2004) Bedrock rivers and the geomorphology of active orogens. An. Revi. Ear. Plan. Sc., v.32, pp Whipple, K. and Tucker, G. (1999) Dynamics of the stream-power model: Implications for the height limits of mountain ranges, landscape response timescales and research needs. J. Geophy. Res., v.104(b8), pp Yin, A., Dubey, C. S., Kelty, T. K., Webb, A. A. G., Harrison, T. M., Chou, C. Y. and Célérier, J. (2010) Geologic correlation of the Himalayan orogen and Indian craton: Part 2. Structural geology, geochronology, and tectonic evolution of the Eastern Himalaya, GSA Bulletin., v.122(3/4), pp Zovoili, E., Konstantinidi, E. and Koukouvelas, I. K. (2004) Tectonic geomorphology of escarpments: The case of Kompotades and Nea Anchialos Faults. Bull. Geol. Soc. Gre., v.36, pp (Received: ; Accepted: )

Morphotectonic Analysis in the Ghezel Ozan River Basin, NW Iran

Morphotectonic Analysis in the Ghezel Ozan River Basin, NW Iran Vahid Hosseini Toudeshki (Corresponding author) Department of Civil Engineering Zanjan Branch Islamic Azad University Zanjan Iran. Tel: 091-266-129-89