Constraints on the tectonic and landscape evolution of the Bhutan Himalaya from thermochronometry

The observed geomorphology and calculated thermal histories of the Bhutan Himalaya provide an excellent platform to test ideas regarding the influence of tectonics and climate on the evolution of a convergentmountain range. However, little consensus has been reached regarding the late Cenozoic history of the Bhutan Himalaya. Some researchers have argued that observed geologic relationships show slowing deformation rates, such that the range is decaying from a geomorphic perspective, while others see the range as growing and steepening. We suggest that a better understanding is possible through the integrated interpretation of geomorphic and thermochronometric data from the comparison of predictions from models of landscape evolution and thermal-kinematic models of orogenic systems. New thermochronometric data throughout Bhutan aremost consistent with a significant decrease in erosion rates, from2 to 3 km/Ma down to 0.1–0.3 km/Ma, around 6–4Ma. We interpret this pattern as a decrease in rock uplift rates due to the activation of contractional structures of the Shillong Plateau, an uplifted region approximately 100 km south of Bhutan. However, low-relief, fluvial landscapes throughout the Bhutanese hinterland record a late pulse of surface uplift likely due to a recent increase in rock uplift rates. Constraints from our youngest thermochronometers suggest that this increase in rock uplift and surface uplift occurred within the last 1.75Ma. These results imply that the dynamics of the Bhutan Himalaya and Shillong Plateau have been linked during the late Cenozoic, with structural elements of both regions active in variable ways and times over that interval.

[1]  R. Bilham,et al.  Miocene rise of the Shillong Plateau and the beginning of the end for the Eastern Himalaya , 2008 .

[2]  Douglas W. Burbank,et al.  Towards a complete Himalayan hydrologic budget : The spatiotemporal distribution of snowmelt and rainfall and their impact on river discharge , 2010 .

[3]  K. Ludwig.  User's Manual for Isoplot 3.00 - A Geochronological Toolkit for Microsoft Excel , 2003 .

[4]  K. Hodges,et al.  Large normal-sense displacement on the South Tibetan fault system in the eastern Himalaya , 2012 .

[5]  Ronald K. Pearson,et al.  Exploring Data in Engineering, the Sciences, and Medicine , 2011 .

[6]  B. Bookhagen,et al.  Abnormal monsoon years and their control on erosion and sediment flux in the high, arid northwest Himalaya , 2005 .

[7]  Roland Bürgmann,et al.  Intraplate deformation of the Indian subcontinent , 2008 .

[8]  Stéphane Bonnet,et al.  Landscape response to climate change: Insights from experimental modeling and implications for tectonic versus climatic uplift of topography , 2003 .

[9]  T. Ehlers,et al.  Large spatial and temporal variations in Himalayan denudation , 2011 .

[10]  K. Whipple.  FLUVIAL LANDSCAPE RESPONSE TIME: HOW PLAUSIBLE IS STEADY-STATE DENUDATION? , 2001 .

[11]  Kip V. Hodges,et al.  Variable shortening rates in the eastern Himalayan thrust belt, Bhutan: Insights from multiple thermochronologic and geochronologic data sets tied to kinematic reconstructions , 2012 .

[12]  J. Suppe,et al.  Mechanics of fold-and-thrust belts and accretionary wedges , 1983 .

[13]  K. Whipple,et al.  Expression of active tectonics in erosional landscapes , 2012 .

[14]  P. Molnar,et al.  Slowing of India's convergence with Eurasia since 20 Ma and its implications for Tibetan mantle dynamics , 2009 .

[15]  R. Parrish,et al.  Exhumation of the Main Central Thrust from Lower Crustal Depths, Eastern Bhutan Himalaya , 2003 .

[16]  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 .

[17]  M. Taylor,et al.  Oblique convergence, arc-parallel extension, and the role of strike-slip faulting in the High Himalaya , 2011 .

[18]  P. Reiners,et al.  Variable exhumation rates and variable displacement rates: Documenting recent slowing of Himalayan shortening in western Bhutan , 2014 .

[19]  B. Grasemann,et al.  Exhumation and uplift of the Shillong plateau and its influence on the eastern Himalayas: New constraints from apatite and zircon (U‐Th‐[Sm])/He and apatite fission track analyses , 2007 .

[20]  R. Parrish,et al.  A short‐duration pulse of ductile normal shear on the outer South Tibetan detachment in Bhutan: Alternating channel flow and critical taper mechanics of the eastern Himalaya , 2011 .

[21]  K. Hodges,et al.  (U‐Th)/He dating of terrestrial impact structures: The Manicouagan example , 2011 .

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

[23]  P. Reiners,et al.  U-Th zonation-dependent alpha-ejection in (U-Th)/He chronometry , 2005 .

[24]  G. Tucker,et al.  Dynamics of the stream‐power river incision model: Implications for height limits of mountain ranges, landscape response timescales, and research needs , 1999 .

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

[26]  M. Trieloff,et al.  Intercalibration of 40Ar–39Ar age standards NL-25, HB3gr hornblende, GA1550, SB-3, HD-B1 biotite and BMus/2 muscovite , 2007 .

[27]  B. Grasemann,et al.  Quantitative morphotectonics of the southern Shillong Plateau (Bangladesh/India). , 2005 .

[28]  K. Hodges.  Tectonics of the Himalaya and southern Tibet from two perspectives , 2000 .

[29]  K. Hodges,et al.  Plio‐Quaternary exhumation history of the central Nepalese Himalaya: 2. Thermokinematic and thermochronometer age prediction model , 2007 .

[30]  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 .

[31]  Jean Braun,et al.  Pecube: a new finite-element code to solve the 3D heat transport equation including the effects of a time-varying, finite amplitude surface topography , 2003 .

[32]  G. Gehrels,et al.  Tectonostratigraphy of the Lesser Himalaya of Bhutan: Implications for the along-strike stratigraphic continuity of the northern Indian margin , 2011 .

[33]  K. Huntington,et al.  Rapid long-term erosion in the rain shadow of the Shillong Plateau, Eastern Himalaya , 2013 .

[34]  J. Ali,et al.  When and where did India and Asia collide , 2007 .

[35]  K. Stüwe,et al.  40Ar/39Ar, pressure, temperature and fission track constraints on the age and nature of metamorphism around the main central thrust in the eastern Bhutan Himalaya , 2001 .

[36]  G. Gehrels,et al.  Preliminary stratigraphic and structural architecture of Bhutan: Implications for the along strike architecture of the Himalayan system , 2008 .

[37]  I. Baillie,et al.  Climate and other factors in the development of river and interfluve profiles in Bhutan, Eastern Himalayas , 2004 .

[38]  M. Clark,et al.  Doing more with less: Bayesian estimation of erosion models with detrital thermochronometric data , 2011 .

[39]  J. Hanchar,et al.  Dating the India–Eurasia collision through arc magmatic records , 2013 .

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

[41]  I. Wendt,et al.  The statistical distribution of the mean squared weighted deviation , 1992 .

[42]  K. Hodges,et al.  Evidence of pre-Oligocene emergence of the Indian passive margin and the timing of collision initiation between India and Eurasia , 2013 .

[43]  J. C. Roddick.  The application of isochron diagrams in40Ar-39Ar dating: A discussion , 1978 .

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

[45]  K. Farley,et al.  The effects of long alpha-stopping distances on (UTh)/He ages , 1996 .

[46]  Leonardo Seeber,et al.  Great Detachment Earthquakes Along the Himalayan Arc and Long‐Term Forecasting , 2013 .

[47]  N. McQuarrie,et al.  Geometry and crustal shortening of the Himalayan fold-thrust belt, eastern and central Bhutan , 2011 .

[48]  K. Hodges,et al.  Metamorphic constraints on the character and displacement of the South Tibetan fault system, central Bhutanese Himalaya , 2013 .