1. Evaporite deformation in the Sierra Madre Oriental, northeastern Mexico: décollement kinematics in an evaporite-detached thin-skinned fold belt Randall Marrett, Department of Geological Sciences, The University of Texas at Austin
Evaporite décollements are important but understudied tectonic elements in fold-thrust belts worldwide. Our fieldwork in the Sierra Madre Oriental of NE Mexico has yielded insights into the complex structure of a thick (~850 m) evaporite décollement. Isoclinal folds, delineated by carbonate intervals within the décollement, dominate the map-scale structure over much of the studied area. North-, NNE- and NE-striking folds dominate, with local refolding by E-striking F2 folds. Some folds are associated with thrust repetition of units. Boudinage is locally important in carbonate units, and can affect members up to 120 m thick. Some evaporite units contain layer-parallel shear zones. The lowermost evaporite interval contains a ~55 m thick shear zone with spectacular banded mylonites. We interpret these structures to reflect two process: décollement-parallel simple shear, and redistribution of décollement material in response to overburden folding (see diagrams at left). These processes may have been partitioned, with simple shear localized in the lowermost part of the décollement.