Structurally-Controlled Hydrothermal Dolomitization

Overview

My Ph.D. research (The University of Manchester, with Cathy Hollis and Ernest Rutter) focused on fault-controlled hydrothermal dolomite bodies hosted in Middle Cambrian strata of the southern Rocky Mountains, western Canada. These dolomite bodies form where hot, mineral-rich fluids exploit deep fault systems, dissolving and replacing the surrounding limestone and precipitating the distinctive banded “zebra texture” that makes them so recognizable in outcrop and hand-specimen. Rather than studying this system with a single method, I built a four-part, complementary research program that moves from descriptions to mechanisms to timing:

Imaging: Shortwave infrared hyperspectral imaging of outcrops to rapidly and non-destructively map multi-phase dolomitization, revealing textural and compositional zoning that was invisible to the naked eye.
Mapping: Basin-scale structural-sedimentological analysis showing how the intensity and style of zebra-textures vary systematically with proximity to the controlling fault systems.
Timing: Direct U–Pb geochronology of dolomite, showing that this hydrothermal fluid flow was coeval with deposition of the world-famous Burgess Shale lagerstätte, raising the possibility that hydrothermal brine seeps helped support the Cambrian ecosystems nearby.
Mechanism: Detailed petrographical and geochemical work resolving the coupled replacement–deformation–cementation processes that build zebra textures band by band.

Key Figures

Schematic cross-section of the Cathedral Formation platform margin showing fault-controlled dolomite bodies at Kicking Horse Pass and Whirlpool Point adjacent to the Burgess Shale Formation. — Regional cross-section of the Cathedral Formation platform margin: Fault-controlled dolomite bodies (pink) at Kicking Horse Pass and Whirlpool Point sit directly adjacent to the Burgess Shale. Fig. 1C, McCormick et al. (2024), *Communications Earth & Environment*, 5, 318.

Outcrop photograph showing a fault zone marked by red dashed lines bordering a dolomite alteration halo. — Outcrop-scale fault zone (red dashed lines) that channeled high-pressure, high-temperature fluids into the surrounding host rock, driving the dilatational fracturing, dissolution, and saddle dolomite cementation that built the adjacent alteration halo. Fig. 2A, McCormick et al. (2023), *Basin Research*, 35, 2010–2039.

Five hand sample photographs showing banded zebra-textured dolomite with replacement dolomite and saddle dolomite cement labeled. — Hand samples showing alternating replacement dolomite (RD) and saddle dolomite (SD) that form “zebra textures”, a diagnostic feature of structurally-controlled hydrothermal dolomite bodies. Fig. 3, McCormick et al. (2023), *Basin Research*, 35, 2010–2039.

Four photomicrographs in plane light and cathodoluminescence distinguishing two generations of replacement dolomite crystals. — Plane polarized light (C, E) and cathodoluminescence (D, F) photomicrographs distinguishing two generations of replacement dolomite (RD1, RD2), the growth zones targeted for U–Pb dating. Fig. 4, McCormick et al. (2024), *Communications Earth & Environment*, 5, 318.

Two U-Pb concordia plots showing dolomite ages of 475.3 million years at Kicking Horse Pass and 488.1 million years at Whirlpool Point. — U–Pb geochronology of the hydrothermal dolomite bodies at the Kicking Horse Pass (475.3 ± 21.8 Ma) and Whirlpool Point (488.1 ± 18.8 Ma) localities, coeval with the deposition of the Burgess Shale. Fig. 5C–D, McCormick et al. (2024), *Communications Earth & Environment*, 5, 318.

Three-dimensional block diagram showing seawater recharge and upwelling crustal fluids mixing along fault networks at depth. — Conceptual model of fault-controlled, hydrothermal dolomitization: Downward-recharging seawater (blue) and upwelling, high-temperature crustal fluids (red) mix along basin-scale fault networks, driving the coupled dissolution-replacement-cementation reactions that form these dolomite bodies. Fig. 6B, McCormick et al. (2024), *Communications Earth & Environment*, 5, 318.

Selected Publications

McCormick, C.A., Rutter, E.H., Corlett, H., Steele-MacInnis, M., Block Vagle, E., Whitaker, F., Hollis, C. (2025). Zebra textures in fault-controlled, hydrothermal dolomite bodies: Coupled mechanisms of replacement, deformation, and cementation. Earth and Planetary Science Letters, 658, 119274.

Ramsey Medal, Tectonic Studies Group View Paper →

McCormick, C.A., Corlett, H., Roberts, N.M.W., Johnston, P.A., Collom, C.J., Stacey, J., Koeshidayatullah, A., Hollis, C. (2024). U–Pb geochronology reveals that hydrothermal dolomitization was coeval to the deposition of the Burgess Shale lagerstätte. Communications Earth & Environment, 5, 318.

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McCormick, C.A., Corlett, H., Clog, M., Boyce, A.J., Tartèse, R., Steele-MacInnis, M., Hollis, C. (2023). Basin scale evolution of zebra textures in fault-controlled, hydrothermal dolomite bodies: Insights from the Western Canadian Sedimentary Basin. Basin Research, 35, 2010–2039.

Harold Reading Medal, British Sedimentological Research Group View Paper →

McCormick, C.A., Rutter, E.H. (2022). An experimental study of the transition from tensile failure to shear failure in Carrara marble and Solnhofen limestone: Does “hybrid failure” exist? Tectonophysics, 844, 229623.

BP Prize, Tectonic Studies Group View Paper →

McCormick, C.A., Corlett, H., Stacey, J., Hollis, C., Feng, J., Rivard, B., Omma, J.E. (2021). Shortwave infrared hyperspectral imaging as a novel method to elucidate multi-phase dolomitization, recrystallization, and cementation in carbonate sedimentary rocks. Scientific Reports, 11, 1–16.

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