Larson, K. and Kellett, D. 2014.   Field guide across the exhumed Himalayan mid-crust along the Tama Kosi and Rolwaling valleys of east-central Nepal. In: (Eds.) Chiara Montomoli, Rodolfo Carosi, Rick Law, Sandeep Singh, and Santa Man Rai, Geological field trips in the Himalaya, Karakoram and Tibet, Journal of the Virtual Explorer, Electronic Edition, ISSN 1441-8142, volume 47, paper 14.

Field guide across the exhumed Himalayan mid-crust along the Tama Kosi and Rolwaling valleys of east-central Nepal

Kyle Larson

Earth and Environmental Sciences, University of British Columbia, Okanagan, 3333 University Way, Kelowna, BC, Canada, V1V 1V7

Dawn Kellett

Geological Survey of Canada, 601 Booth Street, Ottawa, ON, Canada, K1A 0E8


The upper Tama Kosi and Rolwaling valleys in east-central Nepal expose the exhumed midcrustal core of the Himalayan orogen. The region provides an easily accessible transect across, and good exposure of, rocks preserved within that core. Traveling northward from Dolakha in the south to the Tibet border in the north, the rocks record an inverted metamorphic field gradient ranging from chlorite-grade phyllite at lowest structural levels to sillimanite-grade migmatite and leucogranite at the uppermost structural levels. Rocks along this transect are pervasively deformed and preserve dominantly south-directed thrust shear sense indicators. Moreover, they are interrupted by a metamorphic, deformational, and geochronologic discontinuity. Investigation of such structures has helped to reveal the processes responsible for assembly of the Himalayan mid-crust and evolution of the present day kinematic framework. Moreover, integration of available field, microstructural, petrochronologic, and pressure-temperature data has provided insight into the relationship between processes accommodating foreland - hinterland convergence. This field guide describes a number of exposures along the Tama Kosi and Rolwaling valleys in which the deformation, metamorphism, and anatexis at various different structural positions can be observed and compared.

Table of Contents

Accessing the Area
Suggested Itinerary
Geologic Setting
Geology of the Himalaya
Research in the Tama Kosi and Rolwaling region
Field Guide and Suggested Field Stops
Optional Stop - Dolakha (N27.68129˚, E086.07209˚)
Day One - Lower portion of the exhumed metamorphic core
Stop 2 – North of Suri Doban (N27.75690˚, E086.193320˚)
Stop 3 – Melung Augen Orthogneiss (N27.78451˚, E086.21161˚)
Stop 4 – Phyllitic Schist (N27.807603˚, E086.224828˚)
Jagat/Manthale – A Structural Discontinuity
Day Two
Stop 5 – Quartzite (N27.81643˚, E086.22607˚)
Stop 6 – Leucosome-bearing Biotite-rich Schist (N27.88638˚, E086.21870˚)
Stop 7 – Kyanite schistose gneiss (N27.85055˚, E086.21867˚)
Stop 8 – Sillimanite schistose gneiss (N27.87187˚, E086.22228˚)
Day Three
Stop 9 - Sillimanite migmatitic schistose gneiss - (N27.88244˚, E086.23951˚)
Stop 10 - Sillimanite migmatitic schistose gneiss - (N27.88809˚, E086.26345˚)
Stop 11 - Multiple leucogranite phases - (N27.89742˚, E086.27298˚)
Stop 12 – Water-polished exposure of leucogranite relationships - (N27.90151˚, E086.28535˚)
Dogang - (N27.90402˚, E086.28801˚)
Day Four
Stop 13 - Sillimanite migmatite – (N27.90391˚, E086.31406˚)
Stop 14 - Variable Psammitic Gneiss and Quartzite – (N27.90374˚, E086.33268˚)
Stop 15 - Variable Paragneiss and Leucogranite – (N27.90401˚, E086.34673˚)
Day Five
Stop 16 – Quartzo-feldpathic gneiss – (N27.90411˚, E086.37676˚)
Stop 17 – Migmatitic Quartzo-feldspathic gneiss – (N27.89985˚, E086.38164˚)
Stop 18 –Orthogneiss contact – (N27.88344˚, E086.40418˚)
Day Six
Stop 19 – Augen Orthogneiss - (N27.87855˚, E086.43808˚)
Stop 20 – Intruded Metasedimentary Rocks – (N27.87843˚, E086.44570˚)
Stop 21 – Metasedimentary Rocks – (N27.87796˚, E086.45030˚)
Stop 22 – Cross-cut Augen Orthogneiss – (N27.87124˚, E086.44103˚)
Return Trip and Optional Extensions