9. How is magma generated at subduction zones? A. Subduction forces changes in p
ID: 159112 • Letter: 9
Question
9. How is magma generated at subduction zones?
A. Subduction forces changes in pressure and temperature resulting in magma generation.
B. Decompression melting reduces the temperature at which certain minerals will begin to melt thus generating a partial melt.
C. Injected water reduces the melting point of the minerals at the subduction zone causing partial melting
D. hydrous environments lead to decompression, added gas, volatiles, which ultimately form fractional crystallized melts which rise to the surface to produce large pyroclastic eruptions.
10. What are the 2 ways the mantle can generate magma?
A. Partial melting
B. Decompression melting
C. Compression from heat and from the core
D. Convergence at plate boundaries
11. A line of volcanism occurs at subduction zones because of:
A. Mantle convection and partial melting
B. Decompression melting
C. Addition of volatiles and partial melting
D. Subduction
12. You are a geologist trying to determine if the line of volcanic deposits you found formed from a hotspot or from subduction zone volcanism. What would lead you to believe it was a hotspot?
A. Age-relationship of the deposits
B. Sizes of the eruption
C. Number of deposits
D. Viscosity of the lava flows
Explanation / Answer
(9) Magma generated at subduction zones is Subduction forces changes in pressure and temperature resulting in magma generation.
Magma is molten rock which originates deep within the earth. Magma is formed as rock melts at the intense temperatures and pressures present at great depths within the earth. Igneous rocks form when magma rises towards the earth's crust, cools, and solidifies. The name igneous is derived from ignius, a Latin term meaning 'fire'. Most of the rocks which compose the earth, moon, and other planets are igneous in origin.
(10) The two ways the mantle can generate magma are;--
Decompression melting involves the upward movement of Earth's mostly-solid mantle. This hot material rises to an area of lower pressure through the process of convection. Areas of lower pressure always have a lower melting point than areas of high pressure. This reduction in overlying pressure, or decompression, enables the mantle rock to melt and form magma.
Transfer of heat often happens at convergent boundaries, where tectonic plates are crashing together. As the denser tectonic plate subducts, or sinks below, or the less-dense tectonic plate, hot rock from below can intrude into the cooler plate above. This process transfers heat and creates magma. Over millions of years, the magma in this subduction zone can create a series of active volcanoes known as a volcanic arc.
(11) A line of volcanism occurs at subduction zones because of: Subduction
Volcanoes occur in subduction zones, because when a subduction happens, the plate turns into liquid rock. There isn't enough room in under ground for all that liquid rock, so it erupts. After it erupts, it cools, and after a few times, it becomes a cone shape, forming a volcano.
(12) if the line of volcanic deposits formed from a subduction zone volcanism it depend upon the Viscosity of the lava flows.Volcanic activity ranges from emission of gases, non-explosive lava emissions to extremely violent explosive bursts that may last many hours. The types of eruptions determine the relative volumes and types of volcaniclastic material and lava flows, consequently the shapes and sizes of volcanoes. A volcanic event occurs when there is a sudden or continuing release of energy caused by near-surface or surface magma movement. The energy can be in the form of earthquakes, gas-emission at the surface, release of heat (geothermal activity), explosive release of gases (including steam with the interaction of magma and surface of ground water), and the non-explosive extrusion or intrusion of magma. An event could be non-destructive without release of solids or magmatic liquid, or if there is anything to destroy, could be destructive with voluminous lava flows or explosive activity. Destruction usually refers to the works of mankind (buildings, roads, agricultural land, etc.)
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