Age constraints on the deformation style of the South Tibetan detachment system in Garhwal Himalaya
Age constraints on the deformation style of the South Tibetan detachment system in Garhwal Himalaya
Italian Journal of Geosciences (June 2018) 137 (2): 175-187
- absolute age
- Ar/Ar
- Asia
- Cenozoic
- dates
- deformation
- detachment faults
- ductile deformation
- electron probe data
- faults
- Garhwal Himalayas
- granites
- Himalayas
- igneous rocks
- India
- Indian Peninsula
- intrusions
- Main Central Thrust
- Miocene
- Neogene
- plutonic rocks
- plutons
- recrystallization
- Tertiary
- thrust faults
- Uttarakhand India
- South Tibetan Fault
- Malari Pluton
In the Garhwal Himalaya, the Malari granite, a small pluton, intrudes the upper portion of the Greater Himalayan Sequence (GHS) and is deformed in the South Tibetan Detachment System (STDS) shearing. In the present work, we undertook a multidisciplinary approach involving microstructural, chemical and geochronological analyses of the samples in order to constrain the timing of shearing along the STDS. Microstructural observations of samples suggest a switch in deformation features with structural position from the structurally upper samples to the structurally lower one. X-ray maps and electron microprobe analyses reveal a quite uniform chemical composition of muscovite in the three selected samples. (super 40) Ar/ (super 39) Ar muscovite ages constrain the waning stages of ductile deformation: in rocks ductilely deformed by the STDS activity, they record recrystallization at 16.0-16.5 Ma; the age of static muscovite grown after sillimanite at 14.3 Ma post-dates cessation of movement on the STDS and pre-dates the main activity of the Main Central Thrust in the Western Himalaya.