1. A. What are the key compositional differences between seawater and high tempe
ID: 285760 • Letter: 1
Question
1. A. What are the key compositional differences between seawater and high temperature vent fluids? B. What are the mineralogical reactions that either control or contribute to composition of high temperature vent fluids? C. At what temperatures and pressures do these reactions occur? 2. Why is vent fluid salinity an important parameter? 3. Compare vent fluid compositions and alteration mineral assemblages in basaltic and ultramafic rocks - why are they 4. Where is the source of S for the metal sulphides found at vent 5. How does the size of ore deposits compare between fast- and 6. Why are magma chambers important? different? sites? What are the most common sulphides? slow-spreading ridges? Why are they different?Explanation / Answer
1.a) Diffuse venting on the seafloor occurs where high-temperature fluids rising from depth become mixed with cold seawater before they exit the seafloor. The key difference between diffuse and focused vents is how much mixing with seawater occurs before they are released. In other words, the plumbing system of focused vents is well-sealed and transports hot fluid from depth to the seafloor with little or no mixing and the vent fluid comes out of one small pipe. On the other hand, the plumbing of diffuse vents is leaky and allows seawater to mix with the vent fluid and this mixture exits the seafloor over a larger area.
Because of this mixing, diffuse vents are typically low in temperature, with fluids cooler than 200°C (by definition) and usually cooler than about 50°C. Like the high temperature vents, the warm sulfide-rich water provides the foundation for a diverse ecosystem of chemosynthetic organisms which colonize these vent sites. After the 1998 eruption of Axial volcano, diffuse vents were widespread on the new lava flow. White microbial residue along the margins of cracks in the lava surface, in the recesses in lobate flows, and outlining every skylight are evidence for diffuse venting and abundant subsurface microbial growth throughout the lava flow area. Snowblower vents are a unique kind of diffuse vent where white flocculent material is blown out of the seafloor, evidence of a subsurface microbial bloom.
b) This processes responsible for the chemical composition of vent fluids, the formation of sulfide-rich mineral deposits, and the existence of biological communities at hydrothermal vents.
c) As focused high-temperature (350° to 400°C), pressure >150 bar fluids discharge at the seafloor as black smokers, mixing with the surrounding seawater causes metal sulfides to precipitate and form massive sulfide deposits rich in iron, copper, and zinc
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