Wd. Cunningham et al., GEOMETRY AND STYLE OF PARTITIONED DEFORMATION WITHIN A LATE CENOZOIC TRANSPRESSIONAL ZONE IN THE EASTERN GOBI-ALTAI MOUNTAINS, MONGOLIA, Tectonophysics, 277(4), 1997, pp. 285-306
The Gobi Altai is the easternmost extension of the Mongolian Altai and
consists of topographically discontinuous E-W-trending ranges with pe
aks averaging 2000-3000 m in elevation. The region is seismically acti
ve and characterized by prominent E-W left-lateral strike-slip faults
that localize transpressional deformation and uplift along their lengt
hs and at stepover zones. This report summarizes structural field inve
stigations made in the easternmost Gobi Altai to document the structur
al geometry and style of late Cenozoic transpressional deformation in
the region in order to better understand processes of intracontinental
mountain building and the distant intracontinental strain response to
the Indo-Eurasian collision. The Artsa Bogd range marks the northeast
ern terminus of the Gobi Altai and is topographically asymmetric with
a high northern margin marked by N-vergent thrust faults and left-late
ral oblique-slip faults, The northern side of the range is also bounde
d by a foreland basin that contains N-vergent thrust faults and folds
that deform Quaternary sediments, The southern margin of Artsa Bogd ap
pears tectonically inactive but contains S-vergent thrust faults and l
eft-lateral wrench zones. The range appears to have a flower structure
cross-sectional geometry that may reflect transpressional inversion o
f a Mesozoic basin. The isolated, high and narrow Tsost Uul range sout
h of Artsa Bogd occupies a restraining bend position along the left-la
teral Tsost Uul strike-slip fault system. Major faults within the rang
e define a half-fewer structure cross-sectional geometry. To the south
of the Tsost Uul range, the Gobi Bulag left-lateral strike-slip fault
system is marked by small push-up ridges and one major restraining be
nd mountain where the fault steps to the right near its western end. T
hroughout the region, Late Cretaceous-Tertiary basalts and Tertiary an
d Quaternary sediments are deformed by the major fault systems indicat
ing late Cenozoic fault activity. These fault systems and the ranges f
ormed along them occur at fairly regular intervals (approximately 20 k
m) between the North Gobi Altai fault system and the Gobi Tien Shan fa
ult system, two major left-lateral strike-slip faults that cut across
southern Mongolia. Together the faults define a parallel array of disc
rete linear belts of Cenozoic E-W left-lateral transpressional deforma
tion south of the Hangay Dome. The regular spacing of the fault system
s may suggest more uniform distributed left-lateral how at depth. East
ward-directed lower-crustal and lithospheric mantle flow is suggested
by existing seismic anisotropy data for the eastern Gobi Altai and is
believed to be the driving force for the upper crustal deformation.