South Tibetan Detachment System 21/10/2005—16/04/2017

Rocks from the South Tibetan Detachment shear zone, illustrating the typical fabrics. The first set (E03 and ME samples) are from Mount Everest, where the shear zone is ~900m thick, and the rocks are dominated by semipelitic or metapelitic clastic sediments.

The second series (KA samples, John Cottle thesis) is from the Dzakaa Chu, 50 km NE of Mt Everest, where the shear zone is ~1000m wide, and developed mostly in calcareous rocks. The images are arranged in order of increasing structural depth: there is a systematic progression downwards from the top of the zone involving increasing metamorphic grade, and for at least the upper half of the zone, increasing intensity and complexity of the fabrics.
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Sample E03-09 Sample E03-09, plane polarised light, field of view 2.5mm. Collected for us by David Hamilton at the South Col on Mt Everest. This sample evidently came from a...
Sample E03-09
Sample E03-11 Sample E03-11, plane polarised light, field of view 2.5mm. Another South Col sample, but with a markedly different fabric. There is a strong, spaced foliation....
Sample E03-11
Sample E03-10 Sample E03-10, plane polarised light, field of view 5mm. A fine muscovite-biotite phyllite from the South Col. Note the larger quartz grains, probably relics of...
Sample E03-10
Sample E03-10 Sample E03-10, plane polarised light, field of view 1mm. A detailed view of the shear-band fabric, here aligned E-W. It is defined in part by biotite....
Sample E03-10
Sample ME-131 Wager's sample ME-131, plane polarised light, field of view 2.5mm. A biotite-hornblende schist from deeper in the Everest Series, below the North Col, also...
Sample ME-131
Sample ME-131 Sample ME-131, plane polarised light, field of view 2.5mm. S2 fabric cut by shear bands in a biotite-rich part of the sample.
Sample ME-131
Sample ME-131 Sample ME-131, plane polarised light, field of view 1mm. Detail of a shear band, clearly defined by the same biotite-bearing mineral assemblage as the main S2...
Sample ME-131
Sample ME-126 Wager's sample ME-126, plane polarised light, field of view 2.5mm. This is a calcareous phyllite from the lower magin of the
Sample ME-126
Sample ME-126 Sample ME-126, plane polarised light, field of view 1mm. Detail of winged sigma porphyroclast. The porphyroclast is calcite, with an inclusion-rich core,...
Sample ME-126
Sample ME-126 Sample ME-126, plane polarised light, field of view 1mm. Another asymmetric winged porphyroclast showing a very clear contrast between old and new growth, with...
Sample ME-126