GEO 101 Lecture Notes - Lecture 15: Meteoric Water, Connate Fluids, Magmatic Water
23 Jun 2018
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Hydrothermal Rocks
Hydrothermal essentially means “hot water.”Hydrothermal rocks are those rocks
whose minerals crystallized from hot water or whose minerals have been altered by hot
water passing through them. Thus, these rocks are distinct from metamorphic rocks,
which are created by solid state mineral transformations. In fact, many hydrothermal ‐
rocks (such as those that form from hot springs and geysers or crystallize as veins in
cracks in other rocks) actually build up in layers, much as sedimentary rocks do.
Veins result when hot water moves through cracks in the bedrock of the crust. The
water leaches elements from the rocks it passes through. Various minerals are
precipitated on the sides of the crack as the temperatures decrease. The shape and
orientation of the minerals depends on the temperature, pressure, and rate of flow.
When all the available space in the crack has been filled with mineral deposits, the
crack is sealed and the vein is complete.
The water involved in hydrothermal processes is usually either seawater that is moving
downward through oceanic crust near midoceanic ridges or meteoric water. Meteoric
water is water that is derived from the atmosphere as rain or snow and that moves
down into the bedrock from the earth's surface. Water trapped in the original sediments
during deposition and lithification (connate water) can also be included in hydrothermal
reactions but is not a major source of hydrothermal fluid. Magmatic water derived from
magmas is also a minor component.
The water is heated to very high temperatures as it moves deeper into the crust. It
eventually rises again, often removing elements from the rocks it passes through and
carrying them in solution. As the hot water rises toward the surface, it begins to cool.
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Document Summary
Hydrothermal essentially means hot water. hydrothermal rocks are those rocks whose minerals crystallized from hot water or whose minerals have been altered by hot water passing through them. Thus, these rocks are distinct from metamorphic rocks, which are created by solid state mineral transformations. In fact, many hydrothermal rocks (such as those that form from hot springs and geysers or crystallize as veins in cracks in other rocks) actually build up in layers, much as sedimentary rocks do. Veins result when hot water moves through cracks in the bedrock of the crust. The water leaches elements from the rocks it passes through. Various minerals are precipitated on the sides of the crack as the temperatures decrease. The shape and orientation of the minerals depends on the temperature, pressure, and rate of flow. When all the available space in the crack has been filled with mineral deposits, the crack is sealed and the vein is complete.
