Deep-Sea Mineral Deposits

Question

Deep-sea mineral deposits are found on the ocean floor and contain metals such as copper, lead, zinc, silver, and gold. The locations of these deep-sea mineral deposits on Earth are shown in the map below.

From left to right, the illustration titled 'Map 1: World Distribution of Deep-Sea Mineral Deposits' shows the mineral deposit locations at the upper-right edge of Africa next to Asia, between Africa and Australia, the lower-right edge of Asia, the upper-right edge of Australia, the left edge of North America, the upper-left edge of South America, the upper-right edge of South America, and the upper-right edge of North America.

Mining companies can use pumps, bucket systems, and large, robotic digging tools to remove these minerals from the ocean floor. Mining of these minerals provides raw materials for human activities. However, environmentalists are concerned that these mining activities will harm delicate ocean ecosystems.

A hydrothermal vent is another deep-sea feature on the ocean floor. A hydrothermal vent is an opening in Earth’s ocean crust from which very hot water is released. This hot water dissolves minerals in surrounding rock, releasing them into the water. A hydrothermal vent forms when cold seawater flows into cracks in the crust, is heated by hot magma, and then reemerges to form vents on the ocean floor.

The map below shows the locations of worldwide hydrothermal vent activity.

The illustration titled 'Map 2: Locations of Hydrothermal Vent Activity Around the World' shows cracks in Earth's crust as dark blue lines. Orange dots along the blue lines show the locations of recorded hydrothermal activity. From left to right, orange dots appear along the Southeast Indian Ridge south of Australia, along the Western Pacific Back Arc Spreading Centers east of Asia and Australia, along the Northeast Pacific Ridges west of North America, along the East Pacific Rise west of South America, along the East Scotia Ridge southeast of South America, along the Mid-Atlantic Ridge between North America and Asia/Africa, along the Southwest Indian Ridge south of Africa, and along the Central Indian Ridge between Africa and Asia and southeast of Africa.

Constructed Response Question
A. Compare the locations of hydrothermal vents and deep-sea mineral deposits.

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Constructed Response Question
B. Describe TWO geological processes that are most likely occurring in the mineral deposit and hydrothermal vent locations shown on Maps 1 and 2.

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Constructed Response Question
C. Explain why these geological processes likely result in the formation of mineral deposits and hydrothermal vents.

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Answer 1

Constructed Response Question A

Comparison of the Locations of Hydrothermal Vents and Deep-Sea Mineral Deposits

The locations of hydrothermal vents and deep-sea mineral deposits correspond largely to tectonic plate boundaries and geological features in the ocean. Hydrothermal vents are primarily found along mid-ocean ridges, which are formed by the process of seafloor spreading. For instance, the map illustrates orange dots along the Mid-Atlantic Ridge and other ridges and spreading centers where tectonic activity is prominent. In contrast, deep-sea mineral deposits are located near the edges of continents and on isolated seafloor features. While both can be found near plate boundaries, mineral deposits are often positioned on the continental shelves or near subduction zones, suggesting different geological processes are at play.

Furthermore, while hydrothermal vents are clustered along the ridges where new crust is formed, deep-sea mineral deposits are more dispersed and appear at various locations in the ocean basins, often near areas where sediments accumulate and mineralization processes can occur. Thus, there is an intrinsic relationship between the geological features associated with the movement of tectonic plates and the occurrence of both hydrothermal vents and mineral deposits.

Constructed Response Question B

Description of Two Geological Processes

1. Seafloor Spreading: This geological process occurs when tectonic plates move apart from each other, allowing magma to rise from the mantle and solidify to form new oceanic crust. This process is evident along mid-ocean ridges, such as the Mid-Atlantic Ridge. As the plates diverge, it creates the conditions suitable for the formation of hydrothermal vents as seawater interacts with the newly formed crust and is heated by underlying magma.

2. Subduction: This occurs when one tectonic plate is forced beneath another plate, leading to geological activity such as earthquakes, volcanic eruptions, and the formation of mineral deposits. Subduction zones often create areas of increased pressure and heat, which can lead to the concentration of metals and the formation of the types of deposits found in various regions shown on Map 1.

Constructed Response Question C

Explanation of Formation of Mineral Deposits and Hydrothermal Vents

The geological processes of seafloor spreading and subduction are vital to the formation of both mineral deposits and hydrothermal vents due to the conditions they create:

• Hydrothermal Vents: The movement of tectonic plates at mid-ocean ridges causes the formation of cracks in the Earth's crust. Seawater penetrates these cracks, where it is heated by magma. As the hot mineral-rich water is expelled from the vents, it can precipitate minerals as it cools, leading to the deposit of various metals around the vent area. Thus, the heat from magma, driven by seafloor spreading, actively contributes to the formation of hydrothermal vents.

• Mineral Deposits: In regions where subduction occurs, the descension of oceanic crust into the mantle can lead to the melting of rocks and the recycling of minerals back into the crust. This process allows for the concentration of valuable metals such as copper and gold, particularly in regions adjacent to subduction zones. Additionally, the associated tectonic activity can fracture the crust, allowing for the movement and deposition of minerals. Consequently, the geological activity from both seafloor spreading and subduction facilitates the rich formation of mineral deposits in those areas.

In summary, the dynamic processes of plate tectonics, including seafloor spreading and subduction, create the conditions necessary for the development of both hydrothermal vents and deep-sea mineral deposits.