Outcrop photos of rock structures on the road in the Po-Tsangpo river gorge near the Tungmai bridge.
 Photos copyright © 2002-3 W.S.F. Kidd


"Snake on the gneiss"! (estimated to be slightly more than 1 meter long); these are porphyroclastic granitoid gneisses within the zone of sinistral strike slip ductile shear in the northern end of the section near the Tungmai bridge. Migmatitic granitic layers locally cut earlier stages of the foliation. The rocks underwent ductile strain before late cross-cutting granite dikes (see next photo) which are dated by U/Pb on zircons at about 21Ma. The granitoid gneisses of this section are derived from continental basement of the Lhasa terrane and are bounded near the southern end of the section by mylonitic mafic gneisses and schists originating from the oceanic suture between Indian and Asian continental rocks. Elevation about 3100m, close to the "snake line", the upper elevation limit for them in this region.


























Porphyroclastic granitoid gneisses with amphibolite gneiss boudins, containing foliated granitic pegmatitic layers (on right), all crosscut by granite dike (dips gently south from center right to lower left). Two similar granite dikes nearby have yielded 21Ma ages by U/Pb on zircon.


Highly-strained layered quartzofeldspathic and amphibolite gneisses from the southern part of the Po-Tsangpo road section. These show thrust sense of shear with steeply plunging stretching lineation, probably from underthrusting of India in the early stages of the Himalayan colllision.

return to Bill Kidd's Namche Barwa photo index page