Evidence for a wide and gently dipping Main Himalayan Thrust in western Bhutan

The Main Himalayan Thrust (MHT) is the source of great earthquakes that have been documented along the range. Its geometry is a key parameter that influences accommodation of tectonic loading and earthquake magnitudes along the Himalayan Arc. Although seismic images are available for both the western and the central part of the range, this geometry remains poorly constrained for the Bhutanese Himalayas. Here we address this issue using a 10Be cosmogenic nuclides denudation transect across western Bhutan. We observe a wide low denudation rate domain between 50 km and 110 km from the front followed by a strong northward increase. Using a joint inversion of denudation rates, GPS data, and Holocene uplift rates, we interpret this pattern as a consequence of a flat-ramp transition along the MHT. Compared to central Nepal and Sikkim, this location of the ramp suggests a wider decollement, with implications for greater seismogenic potential of the MHT in western Bhutan.

[1]  Vinod K. Gaur,et al.  Crustal structure of the Darjeeling—Sikkim Himalaya and southern Tibet , 2011 .

[2]  D. Grujic,et al.  Miocene structural reorganization of the South Tibetan detachment, eastern Himalaya: Implications for continental collision , 2009 .

[3]  A. Gansser.  Geology of the Himalayas , 1964 .

[4]  M. Kohn,et al.  The age and rate of displacement along the Main Central Thrust in the western Bhutan Himalaya , 2012 .

[5]  K. Hodges,et al.  Active out-of-sequence thrust faulting in the central Nepalese Himalaya , 2005, Nature.

[6]  K. Norton,et al.  Cosmogenic nuclide‐derived rates of diffusive and episodic erosion in the glacially sculpted upper Rhone Valley, Swiss Alps , 2010 .

[7]  Kelin X. Whipple,et al.  Beyond threshold hillslopes: Channel adjustment to base-level fall in tectonically active mountain ranges , 2009 .

[8]  Régis Braucher,et al.  Active tectonics of the eastern Himalaya: New constraints from the first tectonic geomorphology study in southern Bhutan , 2014 .

[9]  D. Granger,et al.  Quantifying rock uplift rates using channel steepness and cosmogenic nuclide–determined erosion rates: Examples from northern and southern Italy , 2010 .

[10]  N. McQuarrie,et al.  Geologic Map of Bhutan , 2011 .

[11]  Jérôme Lavé,et al.  Active folding of fluvial terraces across the Siwaliks Hills, Himalayas of central Nepal , 2000 .

[12]  S. Rani,et al.  Crustal Deformation Associated with Two-Dimensional Thrust Faulting. , 1993 .

[13]  Susan Ivy-Ochs,et al.  Erosion and Exhumation in the Himalaya from cosmogenic isotope inventories of river sediments , 2003 .

[14]  J. Lawrence,et al.  Characterizing the Main Himalayan Thrust in the Garhwal Himalaya, India with receiver function CCP stacking , 2013 .

[15]  G. Tucker,et al.  Numerical and analytical models of cosmogenic radionuclide dynamics in landslide-dominated drainage basins , 2009 .

[16]  G. Hilley,et al.  Restraining bend tectonics in the Santa Cruz Mountains, California, imaged using 10Be concentrations in river sands , 2013 .

[17]  An Yin,et al.  Holocene shortening across the Main Frontal Thrust zone in the eastern Himalaya , 2012 .

[18]  D. Bourlès,et al.  10Be-derived Himalayan denudation rates and sediment budgets in the Ganga basin , 2012 .

[19]  Walter M. Szeliga,et al.  Clockwise rotation of the Brahmaputra Valley relative to India: Tectonic convergence in the eastern Himalaya, Naga Hills, and Shillong Plateau , 2014 .

[20]  Douglas W. Burbank,et al.  Toward a complete Himalayan hydrological budget: Spatiotemporal distribution of snowmelt and rainfall and their impact on river discharge , 2010 .

[21]  Jérôme Lavé,et al.  Fluvial incision and tectonic uplift across the Himalayas of central Nepal , 2001 .

[22]  K. Norton,et al.  Relation between rock uplift and denudation from cosmogenic nuclides in river sediment in the Central Alps of Switzerland , 2007 .

[23]  B. Bookhagen,et al.  Climatic forcing of erosion, landscape, and tectonics in the Bhutan Himalayas , 2006 .

[24]  B. Bookhagen,et al.  Dominance of tectonics over climate in Himalayan denudation , 2014 .

[25]  Ian Parsons,et al.  Surface deformation due to shear and tensile faults in a half-space , 1986 .

[26]  K. Whipple,et al.  Evidence for Pliocene–Quaternary normal faulting in the hinterland of the Bhutan Himalaya , 2013 .

[27]  D. Grujic,et al.  Rapid synconvergent exhumation of Miocene-aged lower orogenic crust in the eastern Himalaya , 2011 .

[28]  R. Stallard,et al.  Denudation rates determined from the accumulation of in situ-produced 10Be in the luquillo experimental forest, Puerto Rico , 1995 .

[29]  Albert Tarantola,et al.  Monte Carlo sampling of solutions to inverse problems , 1995 .

[30]  John Chen,et al.  Underplating in the Himalaya-Tibet Collision Zone Revealed by the Hi-CLIMB Experiment , 2009, Science.

[31]  Gilles Brocard,et al.  What does a mean mean? The temporal evolution of detrital cosmogenic denudation rates in a transient landscape , 2013 .

[32]  Yann Klinger,et al.  Estimating the return times of great Himalayan earthquakes in eastern Nepal: Evidence from the Patu and Bardibas strands of the Main Frontal Thrust , 2014 .

[33]  G. Mitra,et al.  A new kinematic evolutionary model for the growth of a duplex — an example from the Rangit duplex, Sikkim Himalaya, India , 2009 .

[34]  D. Alsdorf,et al.  Crustal deformation of the Lhasa terrane, Tibet plateau from Project INDEPTH deep seismic reflection profiles , 1998 .

[35]  B. Bookhagen,et al.  What controls the growth of the Himalayan foreland fold-and-thrust belt? , 2014 .

[36]  David Whipp,et al.  Geometry and kinematics of the Main Himalayan Thrust and Neogene crustal exhumation in the Bhutanese Himalaya derived from inversion of multithermochronologic data , 2014 .

[37]  Lin Ding,et al.  Convergence rate across the Nepal Himalaya and interseismic coupling on the Main Himalayan Thrust: Implications for seismic hazard , 2011 .

[38]  P. Bierman,et al.  Erosion rates of the Bhutanese Himalaya determined using in situ-produced 10Be , 2015 .

[39]  S. Sapkota,et al.  Imaging the Indian subcontinent beneath the Himalaya , 2005, Nature.

[40]  Xavier Robert,et al.  Control of detachment geometry on lateral variations in exhumation rates in the Himalaya: Insights from low‐temperature thermochronology and numerical modeling , 2011 .

[41]  Larry D. Brown,et al.  Crustal structure of the Himalayan orogen at ∼90° east longitude from Project INDEPTH deep reflection profiles , 1998 .

[42]  Eric J. Fielding,et al.  How steep are the Himalaya? Characteristics and implications of along-strike topographic variations , 2003 .

[43]  P. Tapponnier,et al.  Reconstruction of the deformed collision zone Between India and Asia by backward motion of lithospheric blocks , 2003 .

[44]  E. Doerflinger,et al.  Flexure of the India plate underneath the Bhutan Himalaya , 2013 .

[45]  B. Bookhagen,et al.  Tectonic control on 10Be‐derived erosion rates in the Garhwal Himalaya, India , 2014 .

[46]  A. Heimsath,et al.  Effects of bedrock landslides on cosmogenically determined erosion rates , 2005 .

[47]  Mark T. Lemmon,et al.  Pressure observations by the Curiosity rover: Initial results , 2014 .

[48]  B. Bookhagen,et al.  Impact of glacial erosion on 10 Be concentrations in fluvial sediments of the Marsyandi catchment, central Nepal , 2012 .

[49]  Rodolphe Cattin,et al.  Modeling mountain building and the seismic cycle in the Himalaya of Nepal , 2000 .

[50]  D. Alsdorf,et al.  INDEPTH (International Deep Profiling of Tibet and the Himalaya) multichannel seismic reflection data : Description and availability , 1998 .

[51]  F. Blanckenburg.  The control mechanisms of erosion and weathering at basin scale from cosmogenic nuclides in river sediment , 2005 .

[52]  D. Grujic,et al.  New insight into the South Tibetan detachment system: Not a single progressive deformation , 2012 .