New evidence for syntectonic fluid migration across the hinterland‐foreland transition of the Canadian Cordillera

Abstract

[1] Oxygen isotope data from syntectonic veins, thrust faults, and wall rocks suggest that fluids infiltrated the Western Ranges of the Rocky Mountain foreland from deeper rocks of the Dogtooth Range during Mesozoic contraction. This signifies the first such evidence for kilometerscale fluid migration at the hinterland-foreland transition of the Canadian Cordillera. Fluid infiltration resulted in isotopic depletion in wall rocks and isotopic disequilibrium between veins (fluid) and their host rocks downstream of a lithologic, structural, and isotopic shift between predominantly siliciclastic (Dogtooth Range) and calcareous (Western Ranges) sequences. The shift corresponds with an average d 18 O that is 3.0% higher in the Western Ranges. In the Dogtooth Range, atypically low carbonate values (15.6% ± 0.8% (VSMOW)), and the consistency with which vein signatures approach the average bulk rock d18 O of individual outcrops indicate fluid buffering by a siliciclastic reservoir and outcrop-scale (10 -100 m) fluid circulation. In contrast, rocks and veins in the Western Ranges exhibit a gradational increase in d18 O that extends !14 km eastward and up section from the isotopic shift and possess values that are below or at the low end of typical carbonate compositions (16.2 -20.9% (VSMOW)). Furthermore, veins systematically exhibit lower oxygen values than their host rocks; this implies that the fluids that entered the Western Ranges were in modest disequilibrium with the rocks through which they flowed. We use a one-dimensional reactive transport model to infer that rocks in the Western Ranges experienced a time-integrated fluid flux of 1.1 Â 10 5 mol H 2 O cm À2 (%2.4 Â 10 6 cm 3 cm À2 ) and sluggish reaction kinetics during the flow event.

Variscan veins: record of fluid circulation and Variscan tectonothermal events in Upper Palaeozoic limestones of the Moravian Karst, Czech Republic

“…Veins in groups are, from the oldest A group to youngest C group, gradually less deformed, recrystallized and more regular in shape. Similar features have been reported from quartz veins in siliciclastic terrains (Knoop, Kennedy & Dipple, 2002) and from carbonate veins in collisional belts with thick piles of sediments (e.g. The relationship to solution structures such as stylolite seams is pronounced in many places, pointing to a derivation of the vein material from the host rocks during burial and deformation (Ramsay & Huber, Fluid circulation 1987).…”

“…Open systems are often reported from extensional tectonic regimes (Conti et al 2001), and advection is a dominant fluid flow mechanism for such systems (Jamtveit & Yardley, 1997;Oliver & Bons, 2001). Knoop, Kennedy & Dipple (2002) reported evidence for kilometre-scale and outcrop-scale fluid migration based on the study of the δ 18 O composition of rock and veins in the Canadian Cordillera. Knoop, Kennedy & Dipple (2002) reported evidence for kilometre-scale and outcrop-scale fluid migration based on the study of the δ 18 O composition of rock and veins in the Canadian Cordillera.…”

Structural and isotopic constraints on fluid flow regimes and fluid pathways during upper crustal deformation: An example from the Taemas area of the Lachlan Orogen, SE Australia

“…The preservation of millimeter‐scale isotopic variations in veins confirms that molecular diffusion was unimportant at the scales of interest. Furthermore, the observation that calcite in the immediate wall rock adjacent to veins is not in isotopic equilibrium with the vein calcite indicates that mineral‐fluid isotopic exchange was kinetically controlled, rather than the result of equilibrium exchange and diffusive processes [ Knoop et al , 2002]. …”

“…As externally sourced fluids react progressively with rocks along the flow path, they become more rock‐buffered toward the downstream parts of the system. Reactive transport modeling of isotopic profiles in veins and wall rocks along flow paths can be used to constrain flow directions and fluid fluxes [e.g., Lassey and Blattner , 1988; Bowman et al , 1994; Barnett and Bowman , 1995; Gerdes et al , 1995; McCaig et al , 1995; Abart and Sperb , 1997; Abart and Pozzorini , 2000; Knoop et al , 2002]. The isotopic compositions of vein minerals formed during incremental growth of veins may also preserve a record of changes in fluid chemistry during the evolution of a flow system [ Dietrich et al , 1983; Rye and Bradbury , 1988].…”

Evolution of Cu–Co mineralizing fluids at Nkana Mine, Central African Copperbelt, Zambia

“…The latter two values lie in the field of metamorphic waters (Sheppard, 1986) and such a variation in oxygen isotopic composition is common in metamorphic settings (Gray et al, 1991;Marquer and Burkhard, 1992;Dewaele et al, 2004). Variations are due to different source rocks of the fluids, migration pathways, varying water-rock ratios and the scale of buffering by the rocks (Knoop et al, 2002;Kenis et al, 2005;Berwouts et al, 2008).…”