Italian Journal of Geosciences - Vol. 136 (2017) f.1

Tectonic activity along the inner margin of the South Tibetan Detachment constrained by syntectonic leucogranite emplacement in Western Bhutan

Chiara Montomoli (*), Rodolfo Carosi (**), Daniela Rubatto (***), Dario Visonà (****) & Salvatore Iaccarino (*)
(*) Dipartimento di Scienze della Terra, via S. Maria, 53, 56126, Pisa, Italy.
(**) Dipartimento di Scienze della Terra, via Valperga Caluso, 35, 10125, Torino, Italy. Corresponding author e-mail:
(***) Research School of Earth Sciences, Australian National University, Canberra, Australia.
(****) Dipartimento di Geoscienze, via Gradenigo 6, 35131, Padova, Italy.

Volume: 136 (2017) f.1
Pages: 5-14


In Western Bhutan Himalayas leucogranite dykes emplaced in sub-vertical hybrid fractures that cut across the high-grade rocks of the upper Greater Himalayan Sequence just below to the South Tibetan Detachment. The granitic dykes dip to the north often showing a mylonitic deformation with a top-down to-the-N sense of shear. The high-angle fractures are interpreted to be related to the evolution of the South Tibetan Detachment toward a brittle regime of deformation. U-Pb monazite ages constrain the leucogranite emplacement at 13.9±06 Ma implying that brittle-ductile deformation of the South Tibetan Detachment was active at that time. NNE-SSW to nearly E-W trending large scale antiforms and synforms mapped in NW Bhutan affected the Greater Himalayan Sequence and South Tibetan Detachment only after 14 Ma.


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