Facies and precipitates associated with carbonate-producing hot-springs
Brian Jones
Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T5R 3C8, Can
Brian Jones is a Distinguished University Professor at the University of Alberta, Canada. With his research interests focused largely on all aspects of carbonate sedimentology and diagenesis, he has been involved with projects ranging from the Precambrian dolostones of China to modern carbonates in the Caribbean Sea. One of his main research interests has involved the precipitates found in spring systems with particular emphasis being placed on the high-temperature springs. Based on hot-spring systems in New Zealand, Iceland, Kenya, Chile, China, and Canada, this work has focused on the role that microbes play in these extreme environments and the factors that control the wide array of calcium carbonate precipitates that are commonly found in these settings.
Abstract
Hot springs are commonly located in tectonically active areas like those found in the African Rift Valley, Iceland, New Zealand, and in the Yuannan Province of China where subsurface heat can moderate the temperature and... [ view full abstract ]
Hot springs are commonly located in tectonically active areas like those found in the African Rift Valley, Iceland, New Zealand, and in the Yuannan Province of China where subsurface heat can moderate the temperature and geochemistry of the subsurface groundwater. When ejected at the Earth’s surface, precipitates that form from these hydrothermal waters are characterized by their mineralogical diversity and morphological complexity. Such variability reflects the fact that precipitation is controlled by the interplay of many different variables including the chemistry of the spring water, the rate at which the water cools, degassing of the spring water, and the activity of the microbial populations that are invariably present. These systems are therefore superb natural laboratories for assessing the factors that control the precipitation of the different polymorphs of calcium carbonate as well as the incredible range of crystal forms that can develop.
Precipitation of calcite and aragonite in hot spring environments is controlled principally by saturation levels that vary at all scales. The microbial mats that thrive in these environments commonly play a critical role in the precipitation of these calcite and aragonite. Theses mats, formed of the microbes and copious amounts of exopolysaccharides, are characterized by numerous microdomains (on micron scale) with each domain having its own geochemical signature. Thus, aragonite may be precipitated in one microdomain whereas amorphous calcium carbonate or calcite may be precipitated in an adjacent microdomain. The morphology of the calcite and aragonite crystals that form in hot spring systems is controlled by many different factors, including supersaturation levels, evaporation, degassing, and supercooling that are collectively constitute the “driving force”. As the driving force increases, so the crystal morphology progressively changes skeletal crystals, to dendrite crystals, to spherulitic crystals. Many of these crystals are crystallographically complex with growth patterns that are difficult to determine.
The hallmark of CaCO3 deposits that form in hot spring settings is their mineralogical and crystallographic diversity that commonly reflect subtle, microscale variations in the microenvironments where they formed.
Session
KN2 » Keynote Lecture (10:00 - Tuesday, 23rd June, Pangea)