Fracture mineralization and fluid flow evolution: an example from Ordovician–Devonian carbonates, southwestern Ontario, Canada

Abstract

Petrography, geochemistry (stable and radiogenic isotopes), and fluid inclusion microthermometry of matrix dolomite, fracture‐filling calcite, and saddle dolomite in Ordovician to Devonian carbonates from southwestern Ontario, Canada, provide useful insights into fluid flow evolution during diagenesis. The calculated δ18Ofluid, ΣREE, and REESN patterns of matrix and saddle dolomite suggest diverse fluids were involved in dolomitization and/or recrystallization of dolomite. The 87Sr/86Sr ratios of dolomite of each succession vary from values in the range of coeval seawater to values more radiogenic than corresponding seawater, which indicate diagenetic fluids were influenced by significant water/rock interaction. High salinities (22.4–26.3 wt. % NaCl + CaCl2) of Silurian and Ordovician dolomite–hosted fluid inclusions indicate involvement of saline waters from dissolution of Silurian evaporites. High fluid inclusion homogenization temperatures (>100°C) in all samples from Devonian to Ordovician show temperatures higher than maximum burial (60–90°C) of their host strata and suggest involvement of hydrothermal fluids in precipitation and/or recrystallization of dolomite. A thermal anomaly over the mid‐continent rift during Devonian to Mississippian time likely was the source of excess heat in the basin. Thermal buoyancy resulting from this anomaly was the driving force for migration of hydrothermal fluids through regional aquifers from the center of the Michigan Basin toward its margin. The decreasing trend of homogenization temperatures from the basin center toward its margin further supports the interpreted migration of hydrothermal fluids from the basin center toward its margin. Hydrocarbon‐bearing fluid inclusions in late‐stage Devonian to Ordovician calcite cements with high homogenization temperatures (>80°C) and their 13C‐depleted values (approaching −32‰ PDB) indicate the close relationship between hydrothermal fluids and hydrocarbon migration.

Very hot, very shallow hydrothermal dolomitization: An example from the Maritime Alps (north‐west Italy–south‐east France)

“…A reasonable value for the latter therefore is ca +8‰ SMOW or even lower, and hence perfectly consistent with waters that have strongly interacted with silicate‐rich basement rocks (cf. Haeri‐Ardakani et al ., ,b).…”

“…In recent years, many examples of hydrothermal dolomitization have been documented worldwide (e.g. Boni et al ., ; Lapponi et al ., , ; López‐Horgue et al ., ; Nader et al ., ; Swennen et al ., ; Haeri‐Ardakani et al ., ,b; Hendry et al ., ). In the Alpine chain, several examples of hydrothermal dolomitization come from the Southern Alps (Spencer‐Cervato & Mullis, ; Carmichael & Ferry, ; Carmichael et al ., ; Ferry et al ., ; Ronchi et al ., , ).…”

Hydrothermal fluid flow associated to the extensional evolution of the Adriatic rifted margin: Insights from the pre‐ to post‐rift sedimentary sequence (SE Switzerland, N ITALY)

“…Combining FIs microthermometry and δ 18 O of calcite and dolomite (Horita, ; Kim & O'Neil, ), the oxygen isotope composition of the fluids falls within the range +2 and approximately +12‰ (SMOW). Such isotopic enrichments may be related to evaporation processes (e.g., McKenzie, ), clay mineral diagenesis (e.g., Hensen et al, ) or fluid–rock interaction with silicate minerals (e.g., Haeri‐Ardakani, Al‐Aasm, & Coniglio, ). In the frame of the Adriatic margin evolution, the only reasonable source of fluids feeding the complex fracture‐controlled circulation system was seawater.…”

Diagenetic Pore Fluid Evolution and Dolomitization of the Silurian and Devonian Carbonates, Huron Domain of Southwestern Ontario: Petrographic, Geochemical and Fluid Inclusion Evidence

“…The Michigan Basin has been the subject of several diagenetic studies in the last three decades (e.g., [1][2][3][4][5][6][7][8]). However, very few comprehensive investigations regarding the nature and composition of diagenetic fluids, lateral extent of the diagenetic processes and paragenetic sequence of different types of dolomite within Silurian and Devonian successions in the Huron Domain have been carried out.…”