Genesis of zebra dolomites (Cathedral Formation: CanadianCordillera Fold and Thrust Belt, British Columbia)

Abstract

The late diagenetic zebra dolomites (Middle Cambrian Cathedral Formation: British Columbia, Canada) formed from focalised fluid flow of hot saline fluids ( T h maximum = 180–200 °C, T m,= −18 to −20 °C). δ 18O values vary around − 18.0 ℵ (VPDB) and δ 13C around − 1.35 ℵ. 87Sr/ 86Sr values for the grey (a) replacive dolomite laminae (0.70958 to 0.70970) and for the white, partially replacive laminae and dolomite cement (0.71187 to 0.71228), support involvement of radiogenic fluids which interacted with siliciclastics. Zebra dolomitisation post dates cleavage and is controlled by normal faults. Syn-fracturing dolomitisation in an overpressured regime is invoked for the zebra dolomites formation while the associated coarse crystalline beige dolomites reflect the more passive influx of the dolomitising fluids replacing the host rocks. Overpressuring relates to the fluids that became expulsed during Fold and Thrust Belt development along the paleo-structural Kicking Horse Rim, which defines an area where major paleogeographical changes occurred in the Middle Cambrian. However, the exact age of the dolomites is still uncertain. The fact that MVT mineralisations (Kicking Horse and Monarch deposits), which post-dates zebra formation, occur within a similar structural setting adjacent to the zebra dolomites, suggests that similar fluid flow pathways where re-used several times.