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Trace Element Distribution Analysis in Quartz to Aid in Temperature Profile Constraints in the Sutlej Valley, Himalayas

T. D. Delledera, R. D. Law, and K. T. Ashley
Dept. of Geosciences, Virginia Tech, Blacksburg, VA 24061

Greater Himalayan Series, in the northwestern Sutlej Valley is bounded by the southern Main Central Thrust and to the northern South Tibetan Detachment System. C-axis fabric opening angles, which steadily increases along a 1200-meter structural transect, measured deformation temperatures of dynamically recrystallized quartz along the Greater Himalayan’s. Previous structural studies of these ductile shear contacts have directionally telescoped North-South, indicating a crystal- plastic deformation of quartz.

Qualitative observations of samples collected along the structural transect were observed by cathodoluminescence images under blue filtration (proportional to Titanium-distribution). Samples furthest north from the Main Central Thrust indicate peak metamorphic temperatures of 609°C. In the extensively recovered quartz matrix, higher concentrated Titanium-elongated bands were observed to be surrounded by lower Titanium diffused quartz. Titanium concentrations have no correlation to grain boundaries, since the bands are at an oblique angle to the dominant foliation. Samples closest to the Main Central Thrust are void of these features with preference towards more homogeneous Titanium distribution in matrix grains.

Recent investigations concerning the conditions of garnet growth suggest peak growth around 565°C and 8 kbar. Higher Titanium bands may be paleo-microstructures of subgrain rotation in recrystallized quartz; which resulted from low diffusivities at these temperatures and with the inability to reequilibrate Titanium undergoing recrystallization. The relative timing of deformation occurred at higher temperatures than predicted. Either dynamic recrystallization did not occur at metamorphic peak temperatures or these ribbonfeatures may be the result of other mechanical processes occurring in quartz, despite the extensive recovery that has taken place.

AAPG Search and Discovery Article #90182©2013 AAPG/SEG Student Expo, Houston, Texas, September 16-17, 2013