Evaporite deformation in the Sierra Madre Oriental, northeastern Mexico: dcollement kinematics in an

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Evaporite deformation in the Sierra Madre
Oriental, northeastern Mexico décollement
kinematics in an evaporite-detached thin-skinned
fold beltGareth Cross and Randall
MarrettDepartment of Geological Sciences, The
University of Texas at Austin
Evaporite décollements are important tectonic
elements in fold-thrust belts worldwide, yet have
been little studied. We have carried out
fieldwork in the Potosí uplift of NE Mexico,
where décollement structures are well exposed.
Our fieldwork has allowed us to erect a
provisional stratigraphy for the 1000-1500 m
thick décollement interval (see column at left).
The section contains five thick carbonate members
that act as marker beds for structures. Isoclinal
folds dominate the macroscopic structure,
although boudinage is locally important in
carbonate units and evaporite units may contain
layer-parallel shear zones. Some areas show
multiple fold generations. The lowermost
evaporite interval is a 100m thick shear zone
with spectacular banded mylonites. We interpret
these structures to reflect two process
layer-parallel simple shear, and redistribution
of décollement material in response to
overburden folding (see diagrams at right).