Implications of the ongoing rock uplift in NW Himalayan interiors

12 The Lesser Himalayan duplex exposed in the Kishtwar Window (KW) of the Kashmir 13 Himalaya exhibits rapid rock uplift and exhumation (~3 mm/yr) at least since the Late Miocene. 14 However, it has remained unclear if it is still actively-deforming. Here, we combine new field 15 observations, morphometric and structural analyses with dating of geomorphic markers to 16 discuss the spatial pattern of deformation across the window. We found two steep stream 17 segments, one at the core and the other along the western margin of the KW, which strongly 18 suggest ongoing differential uplift and may possibly be linked either to crustal ramps on the 19 MHT or active surface-breaking faults. Longitudinal fluvial profiles document gradients changes 20 across the entire length of the window, and high gradient changes in the core of the window. 21

. At the same time, we do not agree with the interpretation of surface-breaking faults  The hillslope debris units also contain a few fine-grain sediment layers trapped in between two 216 coarse-grained debris layers (Fig.4e). The town of Kishtwar is situated on this debris flow 217 deposit. For conducting the morphometric analysis, we have used 12.5m ALOS-PALSAR DEM 223 data (high resolution terrain-corrected) (Fig.5a). This DEM data has lesser issues with artifacts 224 and noises than 30m SRTM data, which fails to capture the drainage network properly in areas 225 populated by narrow channel gorges. Topographic relief has been calculated using a 4km moving window (Fig.5b) and the rainfall distribution pattern has been adapted from 12-year averaged 227 annual rainfall data (TRMM data: Bookhagen and Burbank, 2006) (Fig.5c).  229 The drainage network and the longitudinal stream profiles were extracted using the 230 Topographic Analysis Kit toolbox (Forte and Whipple, 2019). An equivalent of 10-pixel 231 smoothing of the raw DEM data has been applied to remove noises from the DEM. The 232 longitudinal stream profile of the Chenab trunk stream was processed with the Topotoolbox 233 'Knickpointfinder' tool (Schwanghart and Scherler, 2014). Several jumps/ kinks in the 234 longitudinal profile are seen and those are marked as knickpoints (Fig.6). A 30m tolerance 235 threshold was applied to extract only the major knickpoints.  237 Global observations across a broad spectrum of tectonic and climatic regimes have 238 revealed a power-law scaling between the local river gradient and upstream contributing area:

Basinwide normalized steepness indices
where S is the stream gradient (m/m), k s is the steepness index (m 2θ ), A is the upstream 241 drainage area (m 2 ), and θ is the concavity index (Flint, 1974;Whipple and Tucker, 1999 275 Specific stream power has often been used as a proxy of fluvial incision or differential 276 uplift along the channel (Royden and Perron, 2013;Whipple and Tucker, 1999  and glacial origin (Owen et al., 2002;Pant et al., 2006). In this study, we used luminescence 321 dating techniques to constrain depositional ages of several fluvioglacial and fluvial sand layers and K-17 taken above the T3 strath level, as well as the sample K-18, taken from above the T1 336 strath level were treated/ measured following the OSL double-SAR protocol. Samples K-01 and 337 K-06 taken above the bedrock strath near the town of Doda were also measured following OSL 338 double-SAR protocol. The aliquots were considered for equivalent dose (ED) estimation only if:

339
(i) recycling ratio was within 1±0.1, (ii) ED error was less than 20%, (iii) test dose error was less than 10%, and (iv) recuperation was below 5% of the natural. Uranium (U), Thorium (Th) and Potassium (K) measured using ICP-MS and XRF (Table 12) in 350 IISER Kolkata. The estimation of moisture content was done by using the fractional difference 351 of saturated vs. unsaturated sample weight (Table 12).  355 The Chenab River has deeply incised the KW ( Fig. 3b and 3e). The LHS rock units base. The KT, southern structural boundary of the window margin accommodating the differential exhumation between window internal and surroundings, is expressed as highly 364 deformed sub-vertical shear bands.

365
Along the traverse of the Chenab River through the KW and further downstream, two 366 prominent stretches along the Chenab River ~20 and ~25-30 km length are characterized by 367 steep channel gradient associated with a large number of rapids (Fig.3b). These steep segments 368 are also characterized by a very narrow channel width (< 30m) (Fig.3b,  schists and phyllites are sparsely present and therefore, they are ignored while plotting the

389
The Higher Himalayan sequence dips steeply away from the duplex (~65° towards west) 390 (Fig.2a, 8a). The frontal nappes of the Lesser Himalaya expose internally-folded greenschist 391 facies rocks. Although at the western margin of the duplex, the quartzites stand sub-vertically, 392 the general dip amount reduces as we move from west to east for the next ~10-15 km (Fig. 8). 393 Near the core of the KW, we observed deformed quartz veins of at least two generations, as well 394 as macroscopic white mica. Near the core of the window, where the river is also very steep and 395 narrow, the rock units are also steeply-dipping towards the east (~60-65°) and are extremely 396 nearly isoclinal and vigorously deformed at places (Fig.2d, 2e). Towards the eastern edge of the 397 window, however, the quartzites dip much gently towards the east (~25-30°) and much lesser 398 folding and faulting have been recognized in the field.

399
The E-W traverse of the Chenab River is completely devoid of any sediment storage.  The longitudinal profile of the lower Chenab traverse (below ~2000 m above MSL) is 521 punctuated by two prominent stretches of knickpoint zones and several minor knickpoints related 522 to change of fluvial gradient (Fig.6). Below we will discuss the potential cause of formation of those major knickpoints in the context of detailed field observation, of existing field-collected 524 structural and lithological data, geomorphic features, rock strength and channel width 525 information (Fig.7). 526 527 Our findings show that the The Himalayan traverse of the Chenab River is characterized 528 by large variations in substrate lithology and rock strength, which cause variations in the fluvial 529 erodibility and form knickpoints on the river profile (Fig.1, Fig.7e). These variations have

Tectonically-controlled knickpoints 540
Compiling previously-published data on regional tectonogeomorphic attributes (Gavillot The knickzone KZ1 (upstream marked by KP2 ~1700 m above MSL) represents the 547 upstream reach of a steepened stream segment of run-length ~18-20 km. The steep river-segment 548 that represents a drop of ~420m of the Chenab River across a run-length of ~15-20 km (Fig.8c).

549
The upstream and downstream side of KP21 is characterized by a change in the orientation (dip 550 angle) of the foliation of the LH bedrock foliation (Fig. 2f, 2g, 8) and channel width (Fig. 7b).

551
Across K1, the dips of the foliation planes change from ~30° to ~60-65° towards east. K1 KP2 552 also reflects a change in the channel width (Fig. 7b). Interestingly, tThe steep segment exhibits a 553 narrower channel and particularly steep valley-walls through the core of the KW. Near the end of 554 the steep segment, we observed intensely-deformed (folded and fractured) LH rocks are exposed 555 (Fig.2d, 2e). We infer two There can be two main possibilities for these field observations folding of Chail nappe to explain the tectonic for the growth and deformation pattern within of the KW. Therefore, we cannot clearly comment whether K1 represents a transition from flat to 570 ramp of the MHT or is it indeed an active out-of-sequence thrust-ramp.

571
On the other hand, the other knickpoint KP3 at the upstream-head of KZ22 nearly 572 coincides with the exposure of the KT (Fig.6). KP32 cannot be a lithologically-controlled 573 knickpoint as it reflects a hard-to-soft substrate transition from LH rocks (R value> 50) to HH 574 rocks (R value< 45) (Fig. 7e). We acknowledge that just across the point K2KP3, there are some  (Fig.8d). Although we didn't find any field evidence of regionally-extensive fault along the N-S traverse of the Chenab River, similar topographic and morphometric pattern can be caused by an 592 active out-of-sequence fault.

593
Both the knickzones, KZ1 and K2 KZ2 are the most-prominent disturbance in the 594 longitudinal profile of the Chenab River and are interpreted to portray spatial distribution of 595 differential uplift due to tectonic deformation.transiently-high specific stream power values 596 (Table 1). This signifies the fact that the knickzones are undergoing much rapid fluvial incision 597 than the rest of the study area. If we consider the fluvial incision as a proxy of relative uplift 598 (assuming a steady-state), we infer that the knickzones define the spatial extent of the areas 599 undergoing differential uplift caused by movement on the fault ramps.

5.
The late Quaternary bedrock incision rates near the western margin of the KW are 808 high 3.1-3.6 mm/yr while away from KW, the incision rates are low (< 1 mm/yr).

809
We argue that the high fluvial incision rate can potentially be linked to    Fig.1a).

1143
The mean R-value±σ for each rock type has been plotted against their spatial extent. We