Compositional Zoning and Crystal Growth Mechanisms in Carbonates: A New Look at Microfabrics Imaged by Cathodoluminescence Microscopy
The interpretation of complexly zoned carbonate cements in terms of diagenetic fluid chemistry remains a central problem in carbonate petrology. In addition to concentric zoning induced by changes in fluid chemistry, synthetic and natural calcite crystals commonly display compositional differences between (1) time-equivalent growth sectors that grew on nonequivalent faces (sectoral zoning), and (2) time-equivalent portions within single growth sectors (intrasectoral zoning). The combination of concentric zoning, intrasectoral zoning, and sectoral zoning, and the wide range of growth forms typical of calcite commonly results in complex microfabrics. Such growth microfabrics are sometimes misinterpreted as evidence for interruption of crystal growth, dissolution, or alteration of pre-existing growth fabrics. The recognition of intrasectoral and sectoral zoning in carbonate cements is, therefore, essential to a correct interpretation of many petrographic fabrics. Examples are presented from synthetic and natural calcite crystals.
KeywordsCalcite Crystal Calcite Cement Carbonate Cement Concentric Zoning Compositional Zoning
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