Stable-isotope geochemistry of syntectonic veins in Paleozoic carbonate rocks in the Livingstone Range anticlinorium and their significance to the thermal and fluid evolution of the southern Canadian foreland thrust and fold belt

摘要

The Livingstone Range anticlinorium (LRA) marks a major hanging-wall ramp where the Livingstone thrust cuts approximately 1000 m (~3281 ft) between regional decollement in the upper part of the Devonian Palliser Formation and the Jurassic Fernie Formation. Prethrusting and folding jasper ± fluorite ± sphalerite veins with halos of altered dolomitic host rock with high Sr/ Sr ratios (0.7094-0.7101) relative to most Paleozoic carbonate rocks (0.7081-0.7091) record percolation of fluids along basement faults that may also have contributed anomalously radiogenic strontium to diagenetically altered Paleozoic carbonate rocks throughout the Western Canada sedimentary basin. Fluid flow that occurred during thrust-propagation folding is recorded by dolomite ± calcite veins, with δ~(18)O values that are similar to those of host rocks (-7.92 to -1.08‰ Peedee belemnite). Anomalously high equilibrium temperatures (250 ± 50°C) as determined by oxygen-isotope thermometry and slightly higher ~(87)Sr/~(86)Sr ratios relative to adjacent host rocks indicate that they formed from formation fluids and hot basement fluids in a rock-dominated system. Calcite veins with very low δ~(18)O values (-18 to -9%o) precipitated along faults that were active while the LRA was transported eastward by underlying thrust faults, uplifted, and rapidly cooled by infiltrating meteoric water. Thrusting created heating in the foreland basin ahead of the deformation because of the influx of thick insulating foreland basin sediments, causing thermal maturation of hydrocarbons. As thrusting deformation advanced through the rocks, infiltrating meteoric waters cooled the rocks and hydrocarbon maturation stopped. Structural traps accumulated hydrocarbons only if they were juxtaposed over both thermally favorable and hydrocarbon-favorable source rocks.