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Geological Society, London, Special Publications; 1993; v. 74; p. 461-473;
DOI: 10.1144/GSL.SP.1993.074.01.31
© 1993 Geological Society of London

High Himalaya

Annapurna detachment fault in the Greater Himalaya of central Nepal

Richard L. Brown & Jeffrey H. Nazarchuk

Department of Earth Sciences, Carleton University, and Ottawa-Carleton Geoscience Centre, Ottawa, ON, Canada K1S 5B6

Displacement on the Annapurna detachment fault (ADF) has exhumed the Greater Himalayan metamorphic sequence in central Nepal. The fault is most likely a continuation of the South Tibetan detachment system recognized elsewhere in the Himalayan orogen.

The characteristics of detachment faulting and the structural and metamorphic histories of the hanging wall and footwall in the Thakkhola region are described. Two stages of normal-sense shearing on the ADF are recognized: the first stage occurred at mid-crustal depth; the most recent detachment faulting on the system was brittle and may have been accompanied by orogen-parallel extension.

First-phase isoclinal folds in the Tibetan sedimentary sequence above the ADF reflect a southwesterly sense of shear and are refolded by spectacular northeasterly verging second-phase folds that have affected a crustal thickness of over 6 km. Third-phase southwesterly directed thrust faults and folds have disrupted the earlier structures but predate the most recent period of normal-sense shearing on the ADF.

The kinematic significance of the northeasterly verging second-phase folds is not clear; these structures may have formed during early motion on the ADF but, alternatively, may reflect older events associated with compression and crustal thickening of the orogen.





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