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Abstract: Growing macroscale fold structures are one of the most dynamic and complex systems in geology, where during fold growth pore fluid pressure, fluid temperature, and fluid composition (PTX) conditions do not remain static but instead vary continually at all points within the deforming fold such that no two points within the fold will have the same deformation or fluid history. These PTX conditions in turn directly affect fluid storage and mobility as well as rock strength, which has direct feedback on the mechanical development of the fold. In this review, we first outline the research methodologies that have yielded significant insights, and review four examples of well-constrained fold-related fluid systems. We then discuss the fluid-related, fold-related, and mesoscopic deformation processes that are relevant to fold-related fluid systems. Finally, we close by presenting several conceptual models for fold-related fluid system structure, and highlighting key areas for future work. [Copyright &y& Elsevier]

Abstract: This study uses fluid inclusions in quartz and calcite veins to characterize the fracture-controlled paleohydrology of a map-scale, evaporite-cored detachment fold in the Sierra Madre Oriental of northeastern Mexico. Field observations indicate that the veins are tectonic in origin, and that they formed in a general sequence that corresponds to four broad stages of progressive folding. We collected samples from each vein stage in various structural and stratigraphic positions across the fold. After determining the mineral paragenesis and origin of inclusions in each sample, we used standard microthermometric techniques to measure the homogenization temperatures (Th ), salinities and eutectic temperatures of the available two- and three-phase aqueous inclusions. Neither Th , salinity nor eutectic temperature varied systematically with inclusion origin or mineral type. The data are also not significantly correlated with structural position or vein type, but are strongly partitioned by stratigraphy, suggesting that the area was a vertically stratified hydrologic system consisting of three regional paleohydrostratigraphic units. An upper unit comprised the Indidura Formation through Difunta Group, and is characterized by Th near 150°C and salinity <5wt% NaCl equivalent. A middle unit comprised the Taraises and Cupido Formations, and is characterized by Th near 150°C and salinities near 12 or 22wt% NaCl equivalent. The lower unit comprised the Zuloaga and La Casita Formations, and is characterized by an average Th near 225°C and salinities in three groups near 12, 22 or 36wt% NaCl equivalent. The preservation of multiple, distinct fluid types in many veins suggests that fracture development during folding and uplift created a second paleohydrologic system that overprinted the vertically stratified system. Fracture-controlled fluid migration in this second system occurred in periodic, repeated, and spatially variable pulses. [Copyright &y& Elsevier]