--> ABSTRACT: Movements of Hydrothermal Fluids Along Three Regional Devonian Dolomite Conduit Systems, Western Canada Sedimentary Basin: Presqu'ile Barrier, Rimbey-Meadowbrook Reef Trend, and Southeast Peace River Arch Fault Conduits, by E. Mountjoy, H. Qing, E. Drivet, X. Marquez, A. Williams-Jones; #91020 (1995).

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Movements of Hydrothermal Fluids Along Three Regional Devonian Dolomite Conduit Systems, Western Canada Sedimentary Basin: Presqu'ile Barrier, Rimbey-Meadowbrook Reef Trend, and Southeast Peace River Arch Fault Conduits

E. Mountjoy, H. Qing, E. Drivet, X. Marquez, A. Williams-Jones

From NE British Columbia to Pine Point over a lateral distance of 400 km, dolomite cements show general trends of decreasing 87Sr/86Sr ratios (0.7106 to 0.7081) and homogenization temperatures (178 to 92°C), with some increase in ^dgr18O values (-16^pmil to -7^pmil PDB). These regional trends suggest that hotter and more radiogenic basinal fluids moved eastward updip along the Presqu'ile Barrier and mixed with cooler ambient formation waters. This barrier appears to have acted as a deeply buried regional conduit system that played an important role in focussing and channeling these basinal fluids.

In the SE Peace River Arch the geochemistry of Upper Devonian Leduc and Wabamun replacement dolomites and dolomite cements are similar. The distribution, geochemistry and fluid inclusion data from the Wabamun replacement dolomites and dolomite cements indicate that they formed from saline hydrothermal fluids (between 100 and 200°C) that moved upwards, possibly as early as the Early Carboniferous, along extensive fault and fracture systems that extend into the underlying Leduc.

Along the Rimbey-Meadowbrook reef trend C and O isotopes of the replacement dolomites are relatively uniform. With increasing burial depth, dolomite and calcite cements are characterized by 1) a slight decrease in O isotopes (-4 to -7^pmil PDB), 2) slightly more radiogenic strontium, and 3) no trend in Sr isotope vs O isotope. This contrasts markedly with the distinctive regional geochemical trends along the Presqu'ile barrier. Pressure corrected fluid inclusion temperatures are 20 to 70°C higher than a geothermal gradient of 30°C/km and temperatures reached during maximum burial in the Early Tertiary. Dolomite cements show no depth trend supporting that they formed during shallow burial from hydrothermal fluids. Four calcite cements follow a 30°C/km geothermal gradient and also require a higher than normal geothermal gradient or the upward movement of hydrothermal fluids. In all regions, large scale movement of hydrothermal fluids appears to be related to tectonic compression and sedimentary loading either during early burial (Late Devonian and Early Carboniferous), or during deeper burial (Late Jurassic and early Tertiary).

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995