The metamorphic core of the Himalayan orogen, or Greater Himalayan seq
uence, is a northward tapering prism bound at the bottom by a N dippin
g family of thrust faults (the Main Central thrust system) and at the
top by a N dipping family of normal faults (the South Tibetan detachme
nt system). Research in the central Annapurna Range of Nepal demonstra
tes a close temporal and spatial association between contractional and
extensional deformation on these bounding fault systems and within th
e metamorphic core throughout much of the Early Miocene. The Main Cent
ral thrust system is represented here by a 2- to 3-km-thick zone of hi
gh strain that developed during two or more episodes of movement. Most
of its displacement was concentrated along the Chomrong thrust, a sha
rp, late-metamorphic discontinuity that places middle amphibolite faci
es rocks of the Greater Himalayan sequence on top of lower amphibolite
facies rocks of the Lesser Himalayan sequence. The earliest demonstra
ble movement on this thrust system occurred similar to 22.5 Ma; the mo
st recent movement may be as young as Pliocene. The oldest element of
the South Tibetan detachment system in this area is the Deorali detach
ment, which appears to have been active at the same time as the earlie
st shortening structures of the Main Central thrust system. Fabrics re
lated to the Deorali detachment are disrupted by a previously unrecogn
ized, SW vergent, thrust structure, the Modi Khola shear zone. The eff
ect of this structure, which is constrained to be between 22.5 and 18.
5 Ma, was to shorten rock packages that had been extended previously d
uring movement on the Deorali detachment. Transition back to a local e
xtensional regime after 18.5 Ma was marked by development of the Machh
upuchhare detachment and related splays. Geologic evidence for rapid,
two-way transitions between contraction and extension in the Annapurna
Range indicates that extensional deformation in convergent settings d
oes not only represent gravitational collapse at the end of an orogeni
c cycle; it also appears to be an important factor in mountain range d
evelopment.