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Integrated Structural and Isotopic Analysis of Veins and Host Rock from the Nuncios Detachment Fold Complex, Monterrey Salient, Mexico

L. Lefticariu
Northern Illinois University, Dept. of Geology, DeKalb, IL

Deformation in the Monterey salient, Sierra Madre Oriental, is dominated by a series of detachment folds that include a 3000 m-thick sequence of Upper Jurassic through Cretaceous carbonates and siliciclastic materials that are detached above a 1000-m evaporitic sequence. The deformation of the sedimentary rocks was accompanied by fluid flow. Fluids may migrate in response to deformation, the paths of migration being controlled by the orientation and distribution of brittle deformation features.

This study is intended to address significant gaps that remain in our understanding of the interaction between pathways available for fluid flow in rocks during folding, using petrologic, geochemical, and structural data to constrain fluid-rock system behavior. My research is focused on (1) identification of the critical pathways along which fluid flow occurred; (2) determination of the physical-chemical properties of the fluid (temperature, pressure, chemical composition) and variations in the open/ closed nature to of the fluid flow system; and (3) delimitation of the evolution of stratigraphically and/or structurally controlled migration pathways and the scale characteristics of the flow event (dimensions of the volume involved).

Preliminary isotopic analyses of veins and host rocks show that the Mesozoic sections contain two main hydrostratigraphic intervals that are not simply related to the lithostratigraphic units. In addition, petrography and isotopic data indicate the presence of multiple distinct fluid events, suggesting a close relation between the pattern of the fluids and the deformation. Within a hand specimen of a single vein we have reported among the largest variations in oxygen isotopes (up to 9 per mil) in calcites precipitated in two distinct fluid events. The results of this study are relevant to the temporal evolution of fluid sources, the timing of fluid migration relative to folding, the role of folds in localizing mineralization and possibly producing and trapping hydrocarbons.

AAPG Search and Discovery Article #90902©2001 AAPG Foundation Grants-in-Aid