Intracrystalline alteration of low-magnesian calcite cement in the Devonian Pillara Formation, Canning Basin, Western Australia
- California State Univ., Northridge, CA (United States). Dept. of Geological Sciences
- Univ. of Cambridge (United Kingdom). Dept. of Earth Sciences
- State Univ. of New York, Stony Brook, NY (United States). Dept. of Earth and Space Sciences
Intracrystalline alteration is present in approximately 25% of the low-Mg calcite cement throughout the lowermost 160 m of the Middle to Upper Devonian Pillara Formation in the Emanuel Range, Canning Basin, Western Australia. A younger, luminescently and chemically distinct calcite phase disrupts primary zonation in older cement and results in irregular, mottled cathodoluminescence (CL). The younger calcite is always in optical continuity with host calcite. Continuous records of Mg, Fe, Mn, and Sr abundances were measured across concentrically zoned, non-CL and yellow-CL cement altered by orange-CL calcite using a new microprobe method designed for high spatial resolution and rapid collection of minor-element abundances in calcite cement. Low-Mg calcite traditionally is regarded as a stable carbonate phase with little tendency toward intracrystalline alteration of chemistry or microstructure. Significant elemental variations measured over small-scale intervals within time-equivalent zones in cement VIa indicate that some parts of the crystal have different chemical potential, which could provide the thermodynamic drive for intracrystalline alteration. Alteration could take place either by a one-step, iterative process of recrystallization or by a two-step, dissolution-cementation process. Lack of micro-collapse features in host calcite, in combination with lack of minor-element memory between host and secondary calcite, support alteration by recrystallization at a high water-rock ratio.
- OSTI ID:
- 7296449
- Journal Information:
- Journal of Sedimentary Research - Section A; (United States), Vol. A64:2
- Country of Publication:
- United States
- Language:
- English
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