People | George
Davis
Fault-Propagation Folding and Meso-Structures
in Andes of Bolivia
Crossing the Several
Scales of Strain-Accomplishing Mechanisms in the Hinterland of
the Central Andean Fold-Thrust Belt, Bolivia
Depictions of structures at outcrop, regional
and tectonic scales enforce horizontal shortening and vertical thickening
as the predominant style of deformation at all scales within the
hinterland of the central Andean fold-thrust belt. Outcrop-scale structures document a
progression of strain that created: (1) flexural-slip folds,
(2) fold flattening via axial-planar cleavage, (3) vertical stretching
via boudinage and late-stage faulting and, finally, (4) kink folding. These
examples of intraformational deformation are generally concentrated
just beyond the tip lines of thrust faults, where fault-propagation
folds and related structures are well developed. Fault-propagation
folding accommodated the accrual of strain indicated by outcrop-scale
structures while the structures themselves indicate how deformation
developed within each individual fold. Fault-propagation fold
geometries at a regional scale emerge from the construction of regional
balanced cross-sections. The sections were drawn with careful
attention to: (1) known map relationships, (2) field inspection
of key contacts, (3) bedding-orientation data, (4) local seismic control,
and (5) principles of balance. The pervasive ESE-WNW shortening
and vertical elongation seen at the outcrop and regional scales developed
during the formation of the Central Andean backthrust belt in the hinterland
of the Andes. The central Andean backthrust belt is a large-scale
west-vergent thrust system along the western side of the Eastern Cordillera
in the generally east-vergent Andean fold-thrust belt of Bolivia. Strain
accrual within this west-vergent zone of deformation is proposed to
be a taper-building mechanism that allowed the fold-thrust belt to
continue propagating eastward.
[McQuarrie, N., and Davis, G.H., 2002, Crossing the
several scales of strain-accomplishing
mechanisms in the hinterland of the central Andean fold-thrust
belt, Bolivia: Journal of
Structural Geology v. 24, no. 10, p 1587-1602.]
|
