RELATIONS BETWEEN FOLDING, FRACTURES, FLUIDS, AND STRATIGRAPHY IN THE MEXICAN SIERRA MADRE ORIENTAL
In addition to these larger-scale relations between fold style and stratigraphy, smaller-scale stratigraphic variations affect the style, distribution, and intensity of mesoscopic structures that developed throughout individual map-scale structures in the fold belt. Joints, veins, cleavage, mineralized faults, and semi-ductile shear zones form to differing degrees in each part of the stratigraphic sequence, and their local characteristics are affected by stratigraphic variables such as lithology, bed thickness, and the apparent frictional strength of bed boundaries.
Stable isotopic and fluid inclusion analyses of quartz and calcite veins exposed along a ~5 km transect across the frontal detachment fold of the Sierra Madre Oriental demonstrate striking stratigraphic control on fluid migration during folding. These analyses suggest a three-part paleohydrostratigraphic system that does not directly correlate with the large-scale, three-part mechanical stratigraphy. In addition, within some paleohydrostratigraphic units, some vein types that form only in certain lithologies, exhibit unique isotopic or homogenization temperature signatures.