Textural and compositional analysis of multiple dolomite generations from the Latemar buildup, Dolomites, northern Italy

• Autores: Kathryn A. Schubel, David R. Veblen
• Localización: Carbonates and Evaporites, ISSN 0891-2556, Vol. 20, Nº. 2, 2005, págs. 148-160
• Idioma: inglés
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• Resumen

  • Fine-scale chemical variations and reaction mechanisms of dolomitization on the Latemar buildup are related to temperatures of, and contact time with, dolomitizing fluids. Dolomites formed at the highest temperatures are the most magnesian and those formed at the lowest temperatures are the most calcian.

    Three generations of dolomite, formed under subaerial sedimentary to subsurface hydrothermal conditions, partially replace Triassic Latemar limestones. Vadose crusts, which cap shallowing-upwards cycles, are partially altered to microcrystalline calcian dolomite (1 to 10 µm crystals, poorly ordered, 52 to 57 mole % CaCO3) that formed at earth surface temperatures. These dolomites are fabric-retentive replacements of allochems and micritic coatings on grains as well as void-lining cements. Subsurface hydrothermal dolomite, formed by platform-scale circulation of hot Triassic seawater, comprises a kilometer-scale mushroom-shaped body of massive replacement dolomite and saddle dolomite cement that crosscuts platform sediments (Wilson et al. 1990; Hardie et al. 1991).

    Temperatures and fluid flow rates of dolomitizing fluids decreased upwards and outwards through the body (Wilson et al. 1990; Hardie et al. 1991). The intensity of dolomitization and reaction mechanisms of dolomitization vary with temperature and fluid flow rate, hence position within the massively dolomitized body. Dolomite from the stem consists of dolomite breccia and saddle dolomite cement. Saddle dolomite cement compositions range from 49 to 55 mole % CaCO3, and dolomite breccia compositions range from 52 to 56 mol % CaCO3. Dolomite from the base of the dolomite body is the least calcian dolomite on the Latemar buildup. Dolomite from the top of the dolomite body is more calcian that that from the base, but less calcian than that in the vadose crusts. Fabric-destructive dissolution and precipitation dominates towards the base of the dolomite body, whereas fabric-retentive dissolution and precipitation is more common towards the top. Cementation takes place throughout the dolomite body.