Publication Date:
2014-04-15
Description:
We quantitatively analyse the spatial pattern of deformation
partitioning and of temporal accumulation of deformation in
the Central Andes (15–26° S) with the aim of identifying those
mechanisms responsible for initiating and controlling Cenozoic plateau
evolution in this region. Our results show that the differential
velocity between upper plate velocity and oceanic plate slab rollback
velocity is crucial for determining the amount and rate of shortening,
as well as their lateral variability at the leading edge of the
upper plate. This primary control is modulated by factors affecting
the strength balance between the upper plate lithosphere and the
Nazca/South American Plate interface. These factors particularly
include a stage of reduced slab dip (33 to 20 Ma) that accelerated
shortening and an earlier phase (45 to 33 Ma) of higher trenchward
sediment flux that reduced coupling at the plate interface, resulting
in slowed shortening and enhanced slab rollback. Because high
sediment flux and transfer of convergence into upper plate shortening
constitute a negative feedback, we suggest that interruption
of this feedback is critical for sustaining high shortening transfer, as
observed for the Andes. Although we show that climate trends have
no influence on the evolution of the Central Andes, the position of
this region in the global arid belt in a low erosion regime is the key
that provides this interruption; it inhibits high sediment flux into
the trench despite the formation of relief from ongoing shortening.
Along-strike variations in Andean shortening are clearly related to
changes of the above factors. The spatial pattern of distribution of
deformation in the Central Andes, as well as the synchronization of
fault systems and the total magnitude of shortening, was mainly controlled
by large-scale, inherited upper plate features that constitute
zones of weakness in the upper plate leading edge. In summary,
only a very particular combination of parameters appears to be able
to trigger plateau-style deformation at a convergent continental
margin. The combination of these parameters (in particular, differential
trench-upper plate velocity evolution, high plate interface
coupling from low trench infill, and the lateral distribution of weak
zones in the upper plate leading edge) was highly uncommon during
the Phanerozoic. This led to very few plateau-style orogens at
convergent margins like the Cenozoic Central Andes in South
America or, possibly, the Laramide North American Cordillera.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Inbook
,
peerRev
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